No P4 plugs into your motherboard. Even if it did... the speed will be about 1/2 the GHz in benchmarks. I have a few i845 systems as proof.

The new P4 CPU consumes more power, makes more heat and may require the ATX12V connector your supply doesn't have. Your old case is likely to not be able to exhaust all the new heat.

Read responses at http://reviews.cnet.com/5208-7586-0.html?forumID=68&threadID=54092&messageID=644604 to fill in the other issues.

Bob