Ram

If the CPU is the brains of the computer, RAM (random access memory) is the muscle. It is the place where the operating system, programs and data in current use are kept, ready to be accessed by the processor. The more RAM you have, the quicker and more powerful your computer is.
If you're faced with a choice between buying a faster processor without much memory, or buying a slightly slower processor with more memory you should take the memory. Having extra RAM will provide a much bigger boost to system performance than a few extra MHz of CPU speed.
While Microsoft's consumer operating system, Windows ME, has a stated requirement of 32MB of RAM you will find the user experience slow and prone to crashes. Any new computer you're considering should have a minimum of 64MB but preferably more. Most retailers offer an upgrade to 128MB for under $100 which is money well spent. If you like to run multiple large applications then 256MB is worth having.