I have a Gainward Geforce2 Pro450 and I could get it to overclock to high & stable. So I added a Sunon 120mm (84 CFM, 35 dBA) intake directly over my AGP slot. This wasn't hard at all. This allowed me to overclock a little more, but not what others were getting. I reallized I needed an outake fan. I had an old delta 120mm (94 CFM, 40 dBA) so I put it on the top of my case. Man is this thing loud, but it keeps the whole system cool. Yes, I'm now clocking the card at 225/480 with no problems.
I don't think you need to go to these extremes. This was my first mod/cooling project. If I was keeping this setup I would add a fan bus to control the loudness. I don't know how your system setup for cooling, but you should have at least one intake in the front, one intake over the AGP and one near the top for outake. 80mm will do okay. I would look at getting quiet fans, unless you don't mind the noise. Also, check your motherboard for 3pin fan headers. This allows you to plug them directly in to your motherboard (if the fan comes in 3pin).
Many sites offer instructions on installing case fans. For each case fan/mod I bought a fan, fan screws, fan grill, rubber strip (covers up mistakes) and power extenion if needed. To install just put the fan on the case where you want it, draw circle from the inside of the fan to the case. This is what you need to cut. I used a jig with thin metal blade. It's good for about 2 cuts. Good Luck!
If you need anything else PM me for more info.