Played the beta for StarCraft 2, which was my first time playing any StarCraft game, and really enjoyed it. Now that the game is out, I have been playing it a lot and wanted to look into upgrading my PC to get the most out of the game. Well, my  procrastination over the last 4 or so years has really come back to bite me. I wanted to get a new graphics card but after reading a performance review for SC2 I found my CPU was the real bottleneck of my system. After looking into getting a new CPU, I came to find that my motherboard does not support the newer CPUs. I am now looking at a major replacement effort for my current PC or buying a new one. Still on the fence on what to do. Any suggestions? 
 
Also, anyone else feeling the pain of upgrading for this game or any others? 
 
The performance review article.

Swapping the mobo out for a new one isn't a major operation, just make sure your power supply is up to the task.

Make sure you check for a BIOS update for your motherboard. Often times they will update it to support newer CPUs.  

If you don't upgrade frequently, then you might consider going with AMD parts since they make their procs backwards compatible with older mobos.

You need to find out what wattage your PSU has first.

" Make sure you check for a BIOS update for your motherboard. Often times they will update it to support newer CPUs.   "

Not to mention you need to know if your Motherboard supports PCIx16 slots for a videocard

I'm assuming that by 'buy' you mean from someplace like Dell, since replacing your motherboard, cpu, memory, etc... is the major part of building a new machine. If you have the cash, just build a new rig. Stuff like case, drives (both optical and hard disk) could be reused (or the old machine could be turned into a house server if you don't have one). Tested did a good guide that included a decent build. If you don't have the cash to replace the main parts (mobo, cpu, memory, gpu) then I'd just wait and save up until you do. Either way, pre-built machines tend to be over priced and loaded with crap ware.
 
I tend to just build a new machine from scratch every few years and then filter the old hardware down into my other computers.

" Not to mention you need to know if your Motherboard supports PCIx16 slots for a videocard "