Naw, just start up your machine and use it for a bit. Once you get the 9800, swap it out and it should work perfectly. When you install OS X, it gives you ALL the graphics drivers you need, so you don't have to have the Radeon in it when you do the installation.
The only thing I can think of where you'd have to have a particular device installed is if you install OS X from a machine with no internal DVD read capability, it will not install the DVD Player application. But that's all I can think of.