cliche

I recently upgraded my computer (Athlon 500 -> XP 2400+) without upgrading the PSU. I can't remember the rating of the PSU in the machine, only that it was quite high in its day (sadly not written on the PSU). I'm generally very happy with the machine but it is slightly flaky. Can anyone tell me what kind of problems an underpowered PSU causes, and any guide on what rating to use if I do need to upgrade. Thanks!

My system:
Athlon 2400+, 512Mb DDR RAM, Asus KT400 Mb
3x IDE HDs (120Gb, 40Gb, 14Gb)
DVD Drive, CDR/W
Geforce 4 Ti4200 AGP Gfx
3x PCI slots filled
Running Win2000 Pro, SP4, fully up to date

Problems:
Internet Explorer crashes frequently
Explorer crashes occasionally
Office works v. slowly (I have a feeling this is a problem with Office, however)
Use of IE rarely results in a reboot on clicking on links


As I said, it generally works absolutely fine - IE is the only real problem and usually just needs reloading (though MS must have received enough 'problem reports' from Dr Watson!)

Thanks