If you have to buy a system, settle on the dual core processor. It is worth the performance and your applications can utilize it. Skip the quad-core processor. For RAM, the 32-bit version of Win XP can only take advantage of about 3MB of RAM. The rest will be unused, but there is no harm in having it installed.

Regardless if you buy a system or not, invest in some disk imaging software, like those that have been mentioned earlier. Image your system onto an external hard drive or some DVDs when you get your system back. Or if you buy a new one, image it the first day you get it, install all of the applications, updates and stuff you want and take another disk image. Then maintain some form of regular backups and annual disk images as software changes. That way you can always restore yourself back to a known good state in little time.

Good luck!