That is an ATX form factor board so it should be very easy to find a replacement. Just make sure your choice is ATX and you shouldn't have any trouble. Just go to
www.newegg.com and look for motherboards with that form factor which is the vast majority of boards out there now a days.
What cpu do you have? Are you wanting to change that as well? If so, I think I would go with a Athlon set up, but that is personal preference.
Motherboards are usually mounted to the case with screws. Just unplug everything from the board and unscrew it. If it mounted with snap ins, just pull it out; be careful. If you know someone who has done it before, have them help you the first time. Make sure your grounded by touching something metal (power supply) before touching anything and also wear a wrist strap. You can get them from Radio shack for little or nothing. I think it is a MUST.
Hope this helps. If you want more specific recommendations, post your specs and what you want to keep etc. I am sure you will find allot of good recommendations here.