Do not use SCSI cables to install IDE devices. (Yes, some incredible moron working for a company I'm familiar with tried to do this.) Actually, it's really easy. Boot hard drive on primary channel set with jumpers as master (can find jumper settings on the website of the drive maker or on the sticker attached to the drive).
CD ROM and CD Writer on secondary channel, one as master one as slave. (again with the jumpers, find the proper settings)
Adding RAM is about the easiest part: find out what kind you need, most likely DIMMs at PC100 or faster for a modern board, get some, and stick them in in the only direction they fit. If you're really lost, take one out of the computer you need more for and go to the computer store with it. Stick it in an anti-static bag though. Static bad.
Always have beer on hand when doing hardware upgrades. Always be prepared to cuss at the computer for a while. These things are necessary in order to convince the system that you know what you're doing, and if you don't drink a beer and swear a lot, the computer will not work.
The US uses 11x V and most of Europe uses the other one. (x being replaced with either 0 or 5, sometimes it's 110 V and sometimes it's 115 V), so if you're in the USA use that one that starts with 11.
Good luck and all.
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kuru
'dancing is the vertical expression of horizontal desire.'
-robert frost