With IDE hard drives being cheap, I thought I'd add a good-sized one and solve any potential future storage problems once and for all. Yes, I suppose I could add one/two extra 80GB hard drive(s) but I thought I'd keep it simple and have only one but of a bigger size. Should make disk imaging/cloning easier and faster should I decide to purchase a newer computer in the future...Come to think of it why do you need a larger drive? 80gb should be fine for Windows 7, a 120gb even better. What do you intend to do with the system that you would need 500+gb of space?
Another option is to put multiple 120Gb (or 80gb since we know for a fact they work with the BIOS) drives in the system and forget about add on cards. Assuming you have a single IDE CD-Rom, you could put in 2 extra IDE drives.