I am not an expert but if you are going to use an XP2400+ shouldn't you have PC2700 or PC3200? I think your memory is going to be the week link.
My vote for mobo is Epox EP-8RDA, RDA+ or RGA+ depending on the options you need. You didn't mention video card so I would assume you want integrated video which means the RGA+. But, the graphics are based on MX440 which is a bit dated.
Try newegg.com or tcwo.com for mobo and CPU. Cases are all over the place. Newegg always has some on sale.
Here is the one I want:
http://www.koolcases.com/aluminumblue.html