Your P2 system may be somewhat upgradable as well. Depending on the board once again, you may be able to take that system to a 466 Celeron, a 600 MHz P3 (Katami core), or maybe even a 1 GHz P3 (Coppermine core).
One last thing, Asus makes both a Deluxe and non-Deluxe A7N8X board. The Deluxe version adds much superior on-board audio, dual lan, firewire, serial ATA, and extra USB 2.0 ports. It is most definately worth the additional $20 over the non-Deluxe version should you choose to go with an nForce 2 Asus board.