Previously, I had an Athlon 2400+ (2.0 GHz) with 640MB of PC2100 RAM. Now I'm running an Athlon 64 X2 3800+ (2.0 GHz) with 2.0GB (Dual Channel 2x 1GB) of DDR400 RAM and the machine boots in under 5 seconds. Yes, I know that a fresh install of the OS might help, but there isn't anything that autostarts on my old machine that isn't on my new machine also (basically just BitDefender).
It's amazing how much faster things can get when all the buses widen and the cpu gains a 'few' transistors =-)
I'm currently developing on a similar machine (XP2400+, 1GB PC2100, GF4Ti4800) and I've been daydreaming about upgrading so I can actually do things while I wait for code to compile. I am now even more tempted than before to actually do so.