what kind of "building a pc?"
do you need suggestions on which part? or do you need instructions on how to plug the parts together? or maybe both?
edit: ok rereading OP gives me the idea of you need both. well to start off, just follow the motherboard's manual, and get an extension cord with a built in fuse and a switch just in case you felt like blowing up the breaker.
first of all, you're saying its gaming then invest lots on GPU but tell us what resolution and/or settings you'll be playing on. still, over spending isn't really a good thing, its all for e-pen when you reach a certain margin.
for the parts, for now, stay away from HDDs, they're 2-3times more expensive than 2months ago, if you're lucky enough you could still find some reasonably priced HDDs.
for the mobo and processor, decide which rig you want, AMD or Intel. WAIT, thats an intel old LGA775.
you'll have to thoroughly research if your choice wasn't its really that bad.
you're after a brandnew rig right? you outa start with either a athlon OR a SNB G620 <--- this rivals that of an E7800.
an i5-2300 will eat a Q9650 alive, yes im serious.
for the GPU, one goooood advantage of wanting an Nvidia over Radeon is that Nvidia has CUDA and Physx, i dont even know what Radeon has advantage of over Nvidia... Nvidia seems to have better drivers too.
the rest is up to your taste, references and reviews, notably brands where their products has less return rates are a priority.
for the how-to-plug-them-together.
*ahem* these goes here, and those goes there, carefully press them together and... voala! you got a lego castle! Jk Jk XD
seriously, its all in the manual.
