the detonator drivers is just like the name of the program so you should be aright with clicking it to remove it all. Usually yeah your computer REALLY wont like two different companies of cards being switched out in your computer (some thing nvidia and ati both put stuff in their drivers so if you switch to the other it'll purposely give you hell) the 5200 model that you have was never meant to gaming, and I think enough people never read that. If you go to nvidias page it's just a 'mainstream model' allowing you to be able to just view 'cinematics' and closer for video editing whereas the 5700 was a 'performance' model and was meant exactly for gaming.
the 6800 could easily be Well MORE than 3 times the power because they say this is the greatest leap in graphical history in quite some time. They have the real-time rendered mermaid going and said they were getting fps of 50-60 and if you tried running the same demo on the best most expensive card out to date before that one (IE. FX5950 Ultra or 9800Pro XT or whatever the ATI equivelant is) would only run the same demo at 3fps......we're talking a HUGE step in graphics processing people not just a little one.
On that note nvidia is gonna release the 6600GT sometime by the end of this year I guess and it'll be 128mb with the new faster DDR3 memory which even the 128mb 6800 doesn't even have. It'll also have 8 pipelines which the ATI equivelant won't.
So basically your conclusion is:
Previous Generation: Go ATI
Next Generation: Go nVidia - They wipe the floor with ATI even their 6600GT will be comparable to the 6800 128mb version and should pack way more power than even the 9800 Pro. The 6600's are supposed to be at like $199 so those look like they'll prove to be a good buy