Hello, sorry for the late reply. It's been kind of chaotic around here for the last few days.
Making a good gaming PC is very similar to making a multimedia-specific computer. It needs as much RAM and CPU as you can provide. Having a good graphic card is also a requirement. It doesn't have to be the latest - but one from last year should be enough. You can go check out this site build-gaming-computers.com where they've outlined all the necessities in detail. In the end it all comes down to how much money you can spare.

Good luck! :)

also. get nvidia card if u want to play games through wine.
ati/amd (prop)drivers are quite a mess and open source driver perf isnt there yet

Thanks for the info Alex! I'll check out that link.

It isn't Linux-specific by any means, but get an SSD.

It's hands down the best upgrade I've done in ages.

Would love an SSD myself, the timings are awesome.

Agreed on the SSD. I recently built a new system then after a couple of months bit the bullet and dropped a SSD in just for the system files. I was instantly converted. ;)