Hals' right. the 1.6A and 1.8A northwood P-4's are what you want, and they are very good for overclocking and highly recomended for it. I haven't got too deep into overclocking yet, because I just got this pc going yesterday. I changed the fsb to 113/38 in the bios and it's running at 2034 mhz{2.03ghz} I'm using the Asus P4S333 with a 1.8A p4, 512MB samsung pc2700,Geforce2mx400{pine-Nvidia} I almost bought the p4s533, and wish I had for the other features it has. you can read all about the asus' at
www.asus.com I'v'e heard a lot of good things about them. also newegg has a inexpensive case called a Maxtop, it has a side and top fan, 2 backfans plus 1 front fan spaces, my cpu seems to stay at 104 degreesF., and the case tempature stay's at room tempature, looks OK too, -$32 ! I bought the samsung pc2700 from
www.buyaib.com they had the best price on it -$50 less than anywhere else. goodluck on your build.