I am about to upgrade to an athlon in the same speed ballpark, and the Asus A7A266 is the mobo I am looking at buying. Here is a review page:
http://www.asus.com/products/motherb...266/index.html
Asus has been recommended to me by several different people for use in conjunction w/ Athlon procs. This one supports both sdram and ddr sdram, which is nice.
As far as the case goes,there are a ton to choose from...I recommend getting a full tower to maximize airspace (and for the spare room for expansion) and at least 300w for the power supply. Here is where I was checking cases at the other day:
http://www.webuildpcs.com/wbpc/scan/...ml?id=ZLsFdmKS
hope this helps a little
Scuba Steve