It takes me about 20-30 minutes to piece together a computer, sometimes less. It's when I install the operating system that it takes longer.... Installing the operating system is pretty easy. All you really need to do is to boot to CD, and then follow the onscreen instructions to get the setup running, and then it'll do the rest for you.
What you really probably need is
160-200GB HD (Seagate if you can)
1GB of DDR
a case with at least 450w power supply
A processor... depending what price range your looking at, you can get anything from a dual core Pentium D (if you decide on this, don't get the 533mhz FSB ones), an AMD Athlon 64 3200/3500/3800 would do ok. Also then you'll get the motherboard... which all depends on what processor your looking at... And you'll get the RAM depending on the board too... For instance, for something like an AMD Athlon 64 3200+ you'll need to get a board that says socket 754 on it, and then your chip would fit onto there (if it was a 3200+... They'll label them on both chips & motherboards, so just make sure they match up. Then you'll look at the motherboards' supported memory, which SHOULD say it in the spec's... That's where you'll decide on what kind of memory you'll need. Also, you probably can be able to transfer your CD roms onto the new system easily, so that's not an issue of needing to be purchased. If your happy with the size of your Hard drives, you don't need to get one. If you need to get a hard drive, get something like a SATA drive if your board will support it, or if not, any other ones will work, try and get one that says 16mb cache on it, and 7200RPM.