Its a good card, a fair bit better than a GTX260 and it'll run all your games maxed out.
Your CPU may hold it back slightly in games that are CPU intensive like BFBC2. Everything else is fine.
Make sure you uninstall all nVidia stuff with driver sweeper before you install your HD5850.
do i run driver sweeper before or after uninstalling the drivers??? thx
one more question, i have to uninstall everything that is from nvidia from the control panel in uninstall a program, right? and just that and then run driver sweeper