I used to work in a computer store about 4 years ago, but haven't since then, so my information may be quite out of date.
You also need to keep in mind what you currently have. Will the new MB work with your power supply, does it have the same memory you have now or are you going to have to invest in new memory as well?
Video card (as mentioned) is a very serious consideration if you are going to be doing a lot of gaming. Since this is the AH BBS, I'm guessing you just might be
I'm sure there are other questions you are going to want to ask yourself before you get started, but those are the only two I could come up with that haven't already been listed.
If it turns out you need a new MB, power suppy, case, memory, and video card, then you are pretty well on your way to a brand new machine. All you are saving at that point is your HD, some cables, and whatever various cards (like network, modem, sound) and drives (such as CD-RW's, DVD etc) you already have.
JoeBWan
VF-17 "The Jolly Rogers"