Building a PC yourself is like pretty easy. If you have ever played with LEGO you should be fine, as long as all the parts match up of course. The PC I buil a month and a half ago was half built by my 13 year old brother while I had to cook. Just like in Legos, when in doubt consult the manual for the motherboard.

Yeah, the cheapest prebuilt you can find will be good enough.

Since it's an office-type/internet computer with no recent games, they'll all be good enough. As long as the CPU is at least a dual-core.

Right, I'll look at it again tomorrow to see if my monitor, keyboard etc will work with it.

You say that but there are issues that can throw you off even if you are experienced at it...especially if you are on the tight budget.

About 6 months ago I picked up a tri SLI Asus AM2 , AM3 board off newegg, a quad Phenom and all the jazz... and the computer would not boot up and was frying my quadcore CPU. It turned out that the board needed a bios flash to support AM3 quad CPUs. Had me stumped for 2 days... and the only reason why I was able to fix it, is because I had a dual core Athlon sitting in a box at home which I could use to boot up the mobo and flash it.

That same thing happened to me. But with an AM2 to an AM2 plus. Got the store where I bought most of my parts to lend me a cpu to reflash with. That won't normally happen, as you can easily buy a board that natively supports the CPU (people on the forum can help him out with that). Everything except the system panel is really easy to install (and that's only hard because the space is so little). I'd also see if you can find someone to test the PSU before you do anything. I had two bad PSU's in one build (both times put into case before testing) before I got one that works.