I would recommend the AMD FX4100 and the ASUS F1A55-M/CSM motherboard. the board can accept faster processors and up to 32 gigs of ram so it has plenty of breathing room.
The 4100 is a quad core processor and is pretty damn fast, if you REALLY need the muscle you can later upgrade to a 6 or even an eight core processor. but realistically most software out there right now doesn't even take advantage of 4 cores much less 8.
for Ram I would suggest starting out with 8 gigs of DDR3. make sure its a single module, this way you can easily upgrade one stick at a time as you need it.
the other upgrade I would suggest would be a Solid state Hard drive, next to the Ram and CPU it will make the most difference in the speed of your computer. solid state drives have really fast response times, I upgraded my CPU and ram and still had a standard HD. once I upgraded the drive to a solid state I was taken back by how much faster programs opened and programs responded.The only drawback is that they can get really expensive as you move into the larger capasities, you might just want to load your OS and the essensials on it and have a second drive of the traditional nature to store all your files. (make sure the drive has a SATA III interface to get the fastest transfer speeds)
so with a FX 4100, 8 or more gigs Ram and a Solid state drive I would be a little frightened if your computing needs made it lag.
oh yes and make sure you have a 64 bit OS. you will need it if you want to take advantage of more then 4 gigs RAM and anything with more 4 cores if you ever want to upgrade past a quad core.
what I have outlined here should cost you about about $500 in parts and software, depending on the size of the solid state drive you pick. that figure also assumes you will just be replacing the mentioned parts and recycling the rest of your desktop. if you are buying a new unit from the store expect to pay about $1500.
I hope this helps,
Don
dupmeister@tri-crescent.com