Try to stay away from Intel Processors, unless they're the new Core-Duo.  They use too much power and don't perform as well as AMD.  I have a 2.8Ghz Intel Pentium Norwood, but that's from three years ago -- when AMD's were the power hogs.

If you don't have a good, hi-resolution monitor, you should invest in one.  I use a 22" NEC MultiSync FP2141SB CRT.  When I got it three years ago, LCDs couldn't touch it.  Maybe that's changed now, but what I have is still state-of-the-art, or close to it.  The point is: a good monitor should last across several new systems.  The monitor makes a big difference in the enjoyment you get from your computer.

Good luck!!