Swash,
My laptop is an old Dell P130, 24Mb RAM, 2Gb Hard drive. It PPRuNes quite well on Win 98 (95 would probably be a bit faster but I have all my machines "standardised" on 98 release 2) but would probably perform better with a bit of extra RAM (if prices weren't so steep for laptop RAM and I didn't have to throw away the existing RAM to fit something bigger!)
So keep with the P90, add a bit of RAM if you can, and it should give you several years of surfing if all you need is that and a bit of email.
(my office machine is a Celeron 800MHz and the desktop at home is a P100 - the power at the office is for big graphics and stuff - not needed for email and surfing!)