kids, kids settle down! PM each other hate mail about CPUs! Sorry mx416, but whenever anyone says anything about processors in this forum, it becomes an AMD vs. Intel war without helping you.
To answer your question, if i were you i wouldn't spend more than $200 on a motherboard (mobo) and CPU combined. That much money alloted would give you a good rig that would last you a fairly long time if you keep using it like you say you will. I would reccommend getting a mobo with onboard sound and maybe video? If you do a lot of things at the same time u might want to get a CPU with either Hyperthreading (Intel) or Hyper Transport (AMD) but that might be kinda expensive too.
If you want an AMD processor, get a socket 764 and no bigger than a 3000+ (don't worry about the GHz since AMDs structure their chips differently). If you want it to be upgradeable in two years or so, get a socket 939 mobo.
If you go Intel, stick with a 478 chipset mobo and nothing bigger than a 3.0 GHz CPU.
If you have more than $200 to spend, then go ahead and get some better stuff just so that your computer will last longer without needing to be upgraded but for now, $200 will do you nice. Hope i can help.