I am currently running a Koha catalog that will eventually contain the contents of my house (maybe not all of it… no one needs to know that there are Celine Dion cds resting within… shh…). The “server” contains an AMD Phenom 9650 quad-core processor, 4 Gigs of A-Data RAM, on an ECS AMD 785G motherboard with a 1TB hard drive and an LG blu-ray/hd-dvd combo drive. Yeah, this was supposed to be my main/gaming computer, but the crappy $20 case kinda broke so I can’t fit my ATI graphics card, or really any other peripherals in it. As such, it’s serving my personal website.
I began with an OpenBiblio catalog, but eventually switched (though you can still find the OpenBiblio catalog mostly devoid of contents linked). OpenBiblio is nice and simple, but I was seduced by the versatility and capabilities of Koha.
I am running Ubuntu 9.10 karmic koala desktop version. I have moved to Lucid Lynx. I love me some Ubuntu!

gaming computers should have multiple cpu cores and a lot of memory to support those heavy graphics ~~`
I know that. I wanted a budget gaming computer. I had an AMD GPU but the case I had broke, so I just converted it into a server. It’s still a quad core CPU and a 2ghz processor is speedy enough for every game on the market even now. Not at the highest quality, but still quite serviceable