It is possible that if (when?) the PSU burns out that it can cause voltage spikes that could fry other components. A friend had a 420W... not sure what brand but not a bottom of the barrel type. His other specs were a 9700Pro, AthlonXP 2100+, 1Gig, 80GB 7200RPM. It had been running fine for over a year I believe, and one day it just blew. The PSU, CPU, Mobo, and GPU all fried (the HD was ok
). He later replaced the PSU with an Antec TP 500, and somehow got all of his components replaced for free from the shop where he bought it...
Basically, if it were me, I'd replace the PSU with a higher wattage model from a reputable company of your choice and not risk frying everything. Plus, if you get a decent enough PSU you can keep it if/when you upgrade.