A midi tower is perfectly fine for ventilation providing its setup right.
But thats getting ahead of ourselves a bit, first thing it to acertain what is overheating.
Run everest home edition to look at the the CPU and case temps, run prime 95 for a while and see what the max load temp is. Also what core is that P4?
I'm guessing the CPU is overheating so some AS5 and possibly and aftermarket cooler is in order.
Intel core I7 920
6GB OCZ platinum 1600
Samsung 1TB F1 Spinpoint
Samsung SM2443BW 24"