Hey pisces7378:
For your computer, your best bet for RAM would be PC133 MHz SDRAM 168-pin DIMMs non-ECC, unless your system supports 184-pin DDR SDRAM which by the sound of what processor you have, it probably doesn't. PC133 is the fastest RAM currently available for your system that's easy to obtain, and most of all, cheap. The non-ECC because for home based PCs, setups generaly use this as it is cheaper, and the two cannot be mixed.
Brand name RAM is the best way to go, as they do better Quality Control on the RAM, and RAM is not one of those you want to try to return. PNY, Kingston, TOshiba, are all good bets. And be sure to ground your body on the chassis of your box simply by touching the metal before you pull out the power cord.
The amount of RAM that you require really depends on the type of work you're doing. When you open an application, that application is using a percentage of Random Access Memory to commit the actions that are currently in process. An average audio editing application could use anywhere from 30 - 60 Mb of your RAM just staying afloat with no processing going on. Say you are using audio tracking software and you are concurrently using software based effects on the incoming signal. This is going to require more RAM to achieve the desired outcome without affecting the incoming/processed signal. If you are using mulitple tracks, say 16+ when doing a mixdown, you need quite a bit of RAM to keep the machine from choking, especially if there are effects on those tracks. This is also keeping in mind that you want to do eveything in realtime, not wait for the computer to catch up to your, thus preventing you from listening to a uninterupted stream of audio. The above example I would not want to try on a machine that has less than 256Mb RAM. If you are not doing 40+ tracks at a time, I wouldn't worry about needing more than 256Mb, but don't try to keep more than a couple of applications open at the same time because like I said, even a dormant application is using RAM; at that said, don't leave a bunch of applications running in your sys tray if you're on Windoz because they're using RAM also.
Hope this helps...