POST a like to info on your system. And, a picture of the inside of the case.
I'm thinking it's a "slim line" case which means
- custom non-standard power supply form factor (measure w x h x L & post,
- Half height video
- restricted length on video (you have to measure and supply this dimension in you post)
- custom limited space for CPU cooler... (limits game play as CPU will get REALLY hot)
If yours is a Dell 430-121B, it's a pretty good size case and will give you more choices of the graphic card. I have a Dell Studio XPS 435MT that has a real compact case and lately, I could upgrade it with a Corsairs 750HX Power Supply and a HD 6870 graphic card; both Add-Ons are making a big difference on performance of my desktop and make it much faster.