make sure you don't buy excess stuff. for example, check to see what onboard capabilities your motherboard has (sound card, graphics card, etc.) and decide if you're satisfied or not.
power cables should come with the case, and IDE ribbons should come with the motherboard, so no worries there. screws and mobo supports should come with the case as well.
when buying RAM, first decide how much you want and how much you're willing to spend. 512 MB is fine, but if u have the money, go for 1 GB. after you've decided, check the highest speed your motherboard supports (usually PC3200). then, check to see if your motherboard is dual channel (this is very important). if you have dual channel, you might want to think of buying Dual Channel RAM. Single Channel will work, but Dual Channel will be much faster if you ever decide to upgrade or use two sticks.
if you're planning to buy a hard drive, buy one that your motherboard supports (e.g. IDE). IDE is way cheaper anyways, and gets the job done. also, you'll need a Windows CD in order to install. i dont know if you can find an OEM version online. if not, you'll have to crank out at least $150 for a full version of Windows.
since you'll need to do a fresh install of Windows, a CD/DVD Drive is also recommended when you're first setting it up.
also, i recommend using a PS/2 mouse and keyboard before you have windows completely installed. some motherboard BIOS's are quirky and wont recognize USB keyboards, and thus will stop loading cuz the system can't find a keyboard. PS/2 keyboards are really cheap, and are available almost anywhere. if you can get your hands on one, buy it, use it for installation, and then return it if you have no more use for it.
when assembling, first and foremost, make sure all the packages contain all that they should. have a screwdriver handy. and also set aside at least two hours of time. trust me, you'll need it. also make sure to keep your manual handy, especially the one for your motherboard. you'll really be thankful if u do that.
there's some post-assembly stuff that you need to take care of, but that's after you've assembled. PM me if you need any help or have anymore questions, i'll be glad to help. i've build computers before, so it shouldn't be a problem.
EDIT:
Sir_Ibi beat me to it
![Sad :(](./images/smilies/icon_sad.gif)
![Laughing :lol:](./images/smilies/icon_lol.gif)
btw, good luck!