Upgrading

I’m getting pretty tired with my slow Toshiba, so i was wondering if it’s of any use upgrading the old thing. It’s an old 3200M Equium with a 450Mhz P3. I want to upgrade (and not buy a new one), because i want to re-use a lot of the stuff. Just got a 80 gig HD and a Lite-on LDW-811S. So i was wondering if anyone could tell me if it’s usefull to upgrade and if so, what i should keep in mind while upgrading. I know that the PSU is 150W which is not enough for a new Mobo or Processor, so i was also wondering if it could be replaced.
Thanx,
Steve
btw the case is 363mm182mm396mm