
You could get a replacement fan but it is unlikely to be worth the time, money and hassle, this is assuming you're using a GF2/Rad7500 type card.

1ghz is very wasteful for a 4200, GF3 or Rad8500/9000 are the cards you really should consider as GF4TI cards will offer very little over these. The only exception would be if you were planning to upgrade the CPU in the next few months, and considering the prices of the AthlonXP this would be very wise. You could get the GF4TI if you wanted as with GF3 or Rad8500/9000 you will be making a compromise as GF3 lacks image quality, dual display, decent TVout/VIVO and the AA isn't quite as good, the Rad8500/9000 cards only lose out in AA but also bring hw DVD playback which both GF3 and GF4TI lack.

So with the abilities and prices of current gfx cards I'd suggest you upgrade. Rad8500-128MB are very good cards and would get my vote if your budget is under $100, GF3 tend to have slightly better perf and much better AA but as stated above also have their drawbacks. Your CPU will hardly limit these cards at all, esp once you use 2xAA and 2xAA on the GF3 or 16tap Aniso on the Rad8500. If you choose the GF4TI4200 then you will certainly want 2xAA/QxAA and 8xAniso! Do give serious consideration to upping your CPU though.