Any AGP slot should be compatable with that card. However, if your really wanting to stay cheap, look for a mobo with onboard video. Some really arn't that bad, and even have an AGP slot for future expansion...
As for desktop cases, I guess first make sure it's ATX. A removable backplane would be nice too, seeing as many new mobo's use ITX or just plain weird setups with the port arrangments ;P
Cooling can be a factor. I should know because my old PIII 733 desktop was like a little heater! Look around, I've seen towers for about $30 with power supplies!