Can I Boot My New Dell 8700 From My Old Dell 400 HDD Running XP SP3

Ok, so my old Dell 400 died. The Hard drive is still good but it has XP SP3 on it. Plus, I've got a few old school VST's and programs that aren't going to run on Windows 8.1. So, I thought I'd put it in my new Dell 8700 and boot from it from time to time if I need to work on an old project using an old program or VST. Can I boot an XP HDD on this computer?

Also, I'd like to be able to select which drive to boot from at start up. What is the best way to make that happen?

Maybe it will boot and load windows and maybe not. 
 
From the viewpoint of the OS version installed on your old hard drive, the only thing that has changed is the hardware. If your old version of XP has the basic drivers to interact with the new motherboard and peripherals, it may boot, and load appropriate drivers. If not then Windows may fail to load or run. A general installation of XP from a retail CD might have loaded and saved unused drivers to the HD. That is much less likely if the OS version came from Dell, as they would have no reason to include drivers for any other hardware than the computer they sold you.  The Dell version was never meant to be used on another computer.
 
A clean installation on the new computer would be preferable if you really need to run XP, but finding installation media and a license for XP now is really problematic.

It may boot but I doubt that it will run very well.  If you just want to get user data off of it, connect it and then just copy from that drive to wherever you want the user data.  You can't copy programs as they must be installed.   There are no Dell supplied Windows XP drivers for the 8700 and probably won't be able to find them for most devices.
 
Best option is to "bite the bullet" and install what you want on the new PC, providing the old XP software is compatible.  I know it is a hassle, but really the best way.   

Sorry, should have been more precise in my original post. It's an XPS 400 and the drives in it are SATA. Heck, I just bought them early last year. I hope what I want to do will work. I have Stienberg's Virtual Guitar on that XP HDD and I don't want go without it. Nor, after buying the new Dell and an audio interface, can I afford new virtual guitar software. Not to mention all the other archaic VST's I have that won't run on 8.1 ... ever. ...lol

I don't have a problem with Windows 8.1. The PC won't arrive until tomorrow. So, outside of my Dell Venue 8 Pro tablet, I don't have any experience with 8.1. It seems like a definite step up from XP, though.

slartabartfast
... and a license for XP now is really problematic.

This could be a showstopper. The license registered in XP is linked to the machine ID of your old computer.
XP will recognize that is it not running on the correct machine, and will most likely shut down immediately.
When I replaced the CPU on my old XP computer, I ran into this. The machine ID is tied to the CPU. At the time, XP was actively supported, and moving the license to the "new" machine was easy enough.
I don't know if it's even possible to get a new license for XP at this point in time.
 
As for VST's, many of the older 32 bit VST's can be bridged.
I kept the original zip files of all of my downloaded VST's on my data drive in the XP machine. That drive is now in an external enclosure($20 from NewEgg), and moving these and project data to  my newer computer has been relatively smooth.
And Cakewalk provides links to download a fresh copy of all the VST's I have from them. Does Steinberg offer that as well?
Also, when you load an old project, Sonar will tell you what effects/VST's are missing. You should be able to find something that is currently available to replace the ones that just will not work anymore.

No problem my friend Merry Christmas to you too.
 
Great to see you around Bob, Merry Christmas brother