When I first obtained a BlizzardPPC/040 I found that my system would run for around an hour perfectly before intermmitently crashing. I found that the 040 was getting worryingly hot (it's the 25mhz version like yours) so I simp;y installed a cheap fan which blows air onto the entire card - this is currently cable-tie fitted to my highest 5.25" bay and aims directly at the card.
Since then I've NEVER had any crashing problems relating to the 040 overheating, even on the hottest of days in the summer. You can pick a suitable fan up at a local PC store or Maplins.
Regarding the noisey PPC fan, it's probably bunged up with muck - I take mine out and clean it once a year. Aside from that it should be fine, it's a bit of a hassle to upgrade it, especially since the standard fan will cool it down just fine as long as it's kept clean.
Hope this helps
Brian
