My Laptop is obviously XP 32 bit, and the Desktop is W7 64 bit. 
I forgot about that hitch. But It matters little for me because the Laptop only records Audio and MIDI data and I don't  insert any VST's at that point. 
I use Sonar 8.5 on both computers. 
But for your situation you'll want all 64 bit OS. 

From what I was told you can install W7 64 bit on a lot of older machines IF you can then find drivers for things like the video card. 
But It might have to be the entry level W7. 
There is a 64 bit version of XP but that might cost you, not worth it. 

 I threw Cakewalk Music Creator on my laptop. I assumed it had a smaller footprint Than Sonar. I think it was a $40 download.
  The projects extensions are the same as in Sonar . Save them as a cakewalk bundle and they open right up.

If the lappy can run SONAR it should be fine for recording a couple of tracks, even w/ a slow drive.  As pointed out above, it is the effects and synths that take CPU, not recording or playing back tracks.  One of the reasons people used to use PCI slots instead of FW was the strain on the CPU FW made.  I used to play plenty of audio back on a 486 computer - as long as I didn't put reverb on the song.  You had to freeze (before there was a freeze function).

The other option is a portable recorder.  You can pick up a tascam for $50 w/ pretty good mics and on mine there is a line in.  But Ive used it to record "intimate"  concerts - piano and vox.  If you watch the levels and massage the files later you can get acceptable playback.  W/ an external preamp and mic, it will do very nice recordings, thank you very much.

Good luck - either way should work.

@

@Fog... I had never heard of Wavsaur. Might not be something I'd use for this if Sonar can work but I always like checking out what's out there. Cheers.

@Cactus... hmm, yeah I'll have to look into what my modem/router thingy can do. I've got another router but I'm giving it to my mom so she can cut off her internet and use her tenant's connection. Cheers.

   I agree with the above, I know you can't afford one right now, but the Tascam DP004 is an awesome recorder with phantom power to boot and 4 AA batteries last a very long time, the only downfall is that it's all 16/44.1k.
   Another option, what I do now on my older laptop, is to use Reaper so I can record 24/48k. I favor using a computer over a stand alone recorder personally, just feels like I have way more control. You can even run Reaper from a thumb drive and, atleast for me anyways, it has been very stable for just tracking audio and minor tweaking. I save all my midi work, mixing, mastering, and heavy effects/synths for Sonar. 
   Reaper is Free to try for 30 days I believe, but I was in a situation like your a while back, where I just did not have the funds to purchase any musical equipment and I was closing in on my 30 days, so I wrote them to see if I could use it a little longer and they basically told me that even after the 30 days I could continue using it, but they would appreciate a payment. It was uncrippled the whole time with only a nag screen when starting up, reminding me my trial was over. After 50 some days of using it I ended up buying it and it really works great if you have an older system you want to put to good use, it's probably one of the lights DAW's available and has some great features. 
   Would I trade in Sonar for Reaper...NO WAY, but for what I'm using it for, it definitely is a great tool. HTH 

@joe... Music Creator was another program I was thinking of if all else fails. In my account it was being offerend for $20. Not sure if that was a special or some kind of crossgrade promo because of all the other stuff I've bought.

@AT... Cool. Good to hear this isn't a rare way of doing things. Makes sense though considering people have been recording digitally for so long. Just wasn't sure if X1/2 would cause a problem. Cheers.

That's the nice thing about Reaper. The $60 they ask for it is next to nothing comparatively and it's really more of a voluntary donation. That was going to be my main DAW until I saw all the goodies Sonar came with at such a low price. Still going to try to learn Reaper at some point though because I'm curious. Cheers.

I'm using an old Toshiba laptop, (2 gig RAM, CPU:  Intel(R) Core(TM)2 Duo CPU  T7100  @ 1.80GHz) when I'm away from my main DAW. 
No problems running 5-10 (and sometimes more) audio tracks and some softsynths. 
I did uppgrade from VISTA to Windows 8 and it gave it a new life. 
I believe that your old laptop would do just fine for the task you're talking about.

I am a very happy Beepster today. Thanks again for all the insight guys. Maybe I can even try doing some PRV composing with some light synths for practice when I don't feel like firing up the big rig.

IT WILL WORK! you don't need to spend money :)