Daveny5, sorry to have been confusing - I was trying to portray myself as someone who normally can install software reasonably well.
My DAW PC is solely for music and not a dual boot system. I have as little as possible installed on there.
My family all use Linux to go on line since we had dialler problems and other security issues (paranoia from a long time ago ... win 95,98, 2000!). I'm not managing any images, as I just reinstall if/when a system becomes compromised. But I do get your point: dual boot seems obsolete at present, it's just a habit; however, I do like to keep myself open to diversity;-)
Thanx for your input on Guitar Rig - I had read somewhere on the forum, that it needs running standalone first, but it's all confusing enough, so I appreciate the help! I'll try the custom install first, and if that's unsuccessful, I'll go for the re-installation ... I only said 'no' to Guitar Rig, because I prefer recording my guitar via mics and didn't think it offered anything I wanted (I never used the Amplitube I got with Sonar 6).

 Beepster,
more thanx! My Sonar X1 was seriously shipped in a sealed box with four dvds, only one of which had a sticker. It was for Dimension Pro and Guitar Rig. It was on dvd 1, that contains the X1 installation. Dimension Pro is on dvd 3. So I was unsuccessfully attempting to enter a Dimension Pro serial for an X1 installation. The Dimension Pro sticker contains no hint at it being for Dimension Pro except that it doesn't begin CXSP, instead it begins CWDM. I found this out after three days of questioning my sanity, when I angrily contacted Cakewalk support. They were very helpful! I think that someone in the shipping department at Cakewalk just packed the dvds in the wrong sleeves.
Thanks for other info. I'm going to have to get to my DAW to see if I can get this tuner (the only thing I want from Guitar Rig ...) - I wonder if I ought to just buy an actual guitar tuner?

GR is nice for a little extra shaping of a mic'd sound sometimes. I have GR5 now though which is WAY better than GR4 LE. Wish they would have tossed Amplitude into my Suite package though. Curious as to how that sounds.

Wow... that's really whack. But as I said my GR sticker was on DVD 1 as well with the X1 S/N. The Dim Pro one was on disc 3 I believe but it actually said DimPro on it. Very strange and yeah... I'd be pretty frustrated about that too. Hope you get it all sorted. Cheers!

I did exactly this a few months ago. According to my notes, I ran the original X1 install and made sure Guitar Rig was checked this time.  The trouble I ran into is that I had previously upgraded to X1 Expanded, which gave me a new serial number and registration code. The X1 installer insists on having valid non-Expanded serial number to install, so I had to revert back to the original X1 serial number. Then, once GR was installed, X1 insisted on re-registering, and neither registration code would work. I ended up looking in the registry to find the serial number, and changing it to the Expanded serial number - then the Expanded registration code worked. Whew! 

If you're not currently running X1 Expanded, all should work fine. If you're running Expanded, you might have to change the serial number in the registry as I did.

AND...if you have X1 Expanded...both 32 and 64 bit installed, you have to edit the serial numbers in the registry in two different places. The one edit won't fix it for both versions.

  I successfully got GR 4 LE installed - thanx for getting me there! I did exactly as xtrumpeter and daveny5 recommended: installed from dvd 1 and deselected everything but GR, then ran GR standalone, registered (or was registering first ...?)
- yet when I insert an audio track in X1 and place GR in the fx bin, I can't see any audio reaching the tuner ... I get sound coming out of my speakers, the track can be armed and recorded into, and GR can be used on the audio there, BUT I can't use it to tune my guitar/bass (neither in standalone GR nor with GR as an inserted effect)!?!

I think I've not understood something in the basic routing/installation of my interface. I'm going into the Hi-Z input of FA-66 input 1, which is the preamp input on the right.
As I haven't been able to get any audio into the PC at all, unless X1 is running, I suspect I haven't set up something in Win7 to make the audio also reach non-X1 software. I tried four different freeware guitar tuners prior to this, but I couldn't get any reading from them despite selecting the FA-66 as audio device. Does anybody know if this is a problem with limited functionality of my interface under Win 7 64bit? Or is there something simple eluding me?

  HA! Found out my mistake: GR has a little (to my old eyes) switch for selecting inputs ... it was on L and my cable is in R. Problem solved for GR standalone = happy hobby musician!!!

  I like GR! Not just the tuner!
I've already used it successfully and happily on bass and guitar tracks directly input via hi-Z - clean sounds only yet: the factory preset 'There Will Be Oil' (or sth. like that) for guitar sounded really good for the arrangement I was trying.
I can run GR standalone and get the sound with amp sims and fx, so playing sounds more authentic than the usual dry hi-Z sound I get; Yet X1 records a dry track directly from the input with no GR influence. Then, if I liked the GR settings I was playing through, I just put GR in the track's fx bin with the desired GR-preset chosen. Or I can play around with other sound enhancements on the 'virgin' track. Very handy.

Two issues, though:
when opening a project, a window informs me that tracks are routed to silent outputs - these are precisely the tracks with GR in their fx bins - but I can hear them, so I don't get the reference to silent outputs!?
My most recent project took over two hours to complete mixdown via 'bounce to tracks'-'entire mix'-'new track', whereas rendering usually only takes a few minutes!?

I've started to go through the 'Sweetwater' optimization suggested by beepster - thanx!

I don't have a solution to your problems but if you like GR4 go to Native Instruments website and try the GR5 demo. It only let's you run it for half an hour but it is a fully functional version and you can download it as many times as you want (I downloaded it a few times at once so I could just reinstall it as soon as the demo ran out without having to fiddle around too much). It's way better than GR4 LE and because you bought Sonar you can buy it for $100 if you like it. So far it's been more than worth it for me. Cheers.