Bullshit galore. I'm installing Catalyst drivers over old ones since the days i owned Radeon 9600 Pro (and later on x1950 Pro, HD4850, HD4870, HD5850, HD6870 and now HD6950). Only thing that changed over the years is that you now don't have to restart after the upgrade. Before you had to. But other than that it works perfectly fine for years. And same applies to NVIDIA as well. Have been updating them with install over the old one since the GeForce 2 MX days (and later GeForce 2 Pro, geForce 4 Ti4200, GeForce 6600GT, GeForce 7300GT, GeForce 7600GT, GeForce 8400GS) and never had any problems. So i'd say i know the drivers prety well.