that p4 HP isnt too horrible a price. i get the same machine for like $700, but well... thats me. its decent machine, that model is kinda old though.
here is what you'll not like about it
its micro atx
the power supply is like 130 watts (stable though as a rock. crazy huh)
i845 SDRAM chipset
geforce2 mx 200
and the hard drive is 5400rpm
but it still a very good system
oh that and the p4 in it is a williamete, might even be socket 423 not sure.