I would reccomend a case. I would think that the HP cases suck ass, as I have seen many compaq, emachines, sony crap cases and they totally suck. I would open it up first to see how the config is in the case.
You can keep most of the optical drives I guess and it SHOULD work. 2400 is pretty good, but if you're going to OC, then I suggest like a 2100 or 1700 on a budget or a 2500 barton for some extra cache + nice OC.
Also, buy some new RAM. The 2100 WILL work, but if you're OCing, then no dice.
don't know anything bout Intel sorry... just have to wait to ask a intel guy here...
BUT I can tell you that if you're on a budget, then AMD IS THE WAY TO GO. Go to pricewatch and compare their prices. I recently bought a 1700 for my folks, and I got it to OC to 2.25Ghz. $43 for a chip that kills a ~$200 intel chip is just plain funny and hilarious to me.
<P ID="edit"><FONT SIZE=-1><EM>Edited by fo_sho on 05/23/03 01:13 AM.</EM></FONT></P>
Stick with the original plan. But take the old mobo and proc to your local second hand computer shop and swap it for a good case and psu. Throw in the old case as well. The video card alone would probably take more power than your old unit can deliver. What ever you do though have a blast.
It should all work, providing your power supply is sufficient. Unfortunately, many HP setups like yours come with a wimpy 180 ~ 230 watt power supply. The 9500 and XP 2400+ are going to require a minimum of 300 watts. Check your power supply--it should say on the side what its output is. Another bitch is that many HPs/Dells/Compaqs come with proprietary cases that won't accomodate a standard power supply. How nice of them.
I would recommend purchasing a decent ATX case and a good, solid 350 watt ATX power supply before anything.