Hard to say how much memory you *need* really, not knowing the rest of your system specs or OS or the apps you intend to run....
Memory is only one critical component necessary for recording on a PC, and for the most part once you've got enough, you don't have to think much about it.
The typical minimum recommended memory size for Win9x, NT4, and Win2k is 128MB. I know I know, that's barely enough for Win2k and can be overkill for Win95...but it'll get you there. Really though, 256MB is usually an optimal size.
You might be in luck...if your machine uses SDRAM (most PII and PIII class machines) then 256MB can be had for under $50 from places like crucial.com (highly recommended!).
Before you go hit the buy button, however, you'll need to post your full system specs.
The bare minimum machine for recording, IMHO, would be a PII-350Mhz, 20GB 7200RPM hard drive, and 128MB RAM....of course all that means nothing. A shitty motherboard will kill even the most statistically impressive systems...a poorly designed video card can cause performance issues....and so on and so forth. So let's just hear what you've got and see what we can do from there.
Slackmaster 2000