Use the P1 as your ADSL router/firewall - it'll be good for that (and not much else these days). Run FreeSCO on it (
http://www.freesco.org/ ) - which is designed specifically for this situation - easy to install, runs off one floppy, doesn't change your hard drive (you can actually run it off a FAT hard drive too {faster boot} if you want, without damaging your Windows installation).
The P2 is linked to the P1 by a crossover and off you go.
If it works, you're away. If it doesn't you've lost nothing.