You can fit a low-profile heatsink + fan inside a Cube without any issues, and make a cardboard duct so the hot air is expelled upwards and out of the case.
The Apple OEM Radeon 7500 is a direct fit and a nice card, but you will of course need to modify the back bracket and add a heatsink to the card (I bodged up one from a Radeon 8500). Any card "better" than the Rage 128 will need a fan; you're pushing it with just a base fan installed. In mine I've a slow base fan and the graphics card fan runs @ 7V.
Just to note, the Apple OEM Geforce 3 will fit but it's very hot (that's with a fan!) and far too expensive to bother about.
The cream of the crop is a Mac flashed nVidia 6200, which if you can find the correct one on eBay will fit fine and supports Core Image and high resolutions/dual displays. This will cost you around $100, and is well worth the coin
So the main options are
- Apple OEM Radeon 7500 (cheap, decent speed, ADC monitor connector)
- Apple OEM Geforce 2 MX (hot running, needs a fan, decent performance)
- PC flashed Geforce 2 MX (cheap as)
- PC flashed nVidia 5200/5500 (cheap, hot, Quartz Extreme)
- PC flashed nVidia 6200
... there are other cards that will fit (Radeon 8500, Geforce 3 PC) but you either need to relocate the VRM or buy a Gigadesign VRM which cards can slide easier into, and I'm not a fan at all of the Gigadesign VRM
JB