Looking for a new upgrable system

I've being out the loop for processors and pc parts in general for a couple of years now, I'm currently running a socket 939 Opteron chip and whilst its still reasonably fast, its starting to struggle a bit in games.

I'm working on a bit of a budget here so I would rather get an expensive motherboard and reasonable processor and replace it at a later date, I've read in numerous places that intel are working on a new i7 processor or something but they sound like the boards are going to be really expensive when they get released?
Would these new motherboards stand up to another round of processors or would I be best of going for a core 2 duo or Phenom?
Do the AMD boards limit you to a x3 or x4 or can you swap between them? I hear there isn't much point getting quad core right at the moment?
Are there any particular chipsets to aim for or avoid?

The system would mostly be used for gaming (Crysis and World of Warcraft mainly) and my budget for a board could stretch to about £150 for a motherboard and £150 for a cheap chip at current prices)

Sorry for so many newbish questions, I appreciate any help you can give.

Nothing you say makes any sense. You want a rig that can run Crysis, the slowest gaming hog to date and WoW.... Could you pick two games more dissimilar in performance buckets? WoW can run on a Dell from the 90's.

You dish on a dual core Opteron, which I personally use at 1600x1200 in on-line and off line games and runs just fine...sure some things get slow...but at 2.8GHz it never gets that slow and other CPUs get just as slow in those same spots, even fast C2Ds.

You don't really ask any question so you aren't going to really get an answer, but I can tell you that something is wrong with your rig if you cant get a fast dual core Opteron with 2G of RAM and a fast video card to perform as well as the latest and greatest.

But hey, if you were to build new TODAY. Get a Intel quad-core with DDR3, for the lulz.

If you are insisting on high FPS in Crysis, all other concerns are secondary and you must build the fastest rig you can afford, which will still be inadequate for high levels.

The dual-core Opteron 180 has a stock speed of 2.6GHz, 2.8GHz is trivial at 218 x 13. Perhaps you have a slower single core model, which is underpowered in todays games. Even the dual core Opteron 170 is 2.4GHz and clocks up just as easily, good luck finding either model!