Fran, I am almost certain any computer you buy today will have sufficient resources or can be upgraded to handle anything the soft synth world can throw at you. Here are some things to look at:
2 Hard Drives, 7200rpm, 8 mb cache
You need this if you are going to run heavy duty samplers like Kontakt, GigaStudio, etc. This is to accommodate streaming from a hard drive without crackles & pops. Two hard drives are needed to achieve this (one for the applications & OS and the other for your samples).
Sound Cards
At some point you may wish to add one of the so-called professional sound cards, e.g., RME, M-Audio, Frontier, Echo and so on.
RAM
In future you may wish to add some more RAM to say 2 GB. This will speed up your computer.
Processor
A short few years ago it was safer to get a Pentium over any other including AMD for music or multimedia applications. Today this is less of an issue.
Again I think you should have no problem. Just ensure you can build it up to meet your future needs re: soft synths.
[This message has been edited by Frank L. Rosenthal (edited 06-11-2005).]