Stuttering caused by video drivers

[Viper2035]

Hello everyone!
I wasn't sure if should have posted this in the bug section because I'm not sure it's a bug.
So these are my system specs:
- Asrock K10N78m
- AMD Phenom 2 X2 550 @ 3.1Ghz
- Sapphire HD4650 (1Gb)
- 2 Gb RAM
I've been experiencing stuttering every 5 seconds or so. Here is what I tried:
- All compatibility modes
- Overclocking and underclocking video card
Since I thought the problem was graphic related I tried using the onboard geforce 8100 card: I was surprised when I found out it ran smoothly.
Then I tried to run the game with the AMD card again but only with windows' standard drivers and the stuttering had disappeared! As soon as I intall the Catalyst Suite the stuttering comes back.
[I would keep the card without drivers but the problem is it has no support for OpenGL (without catalyst) so games like Minecraft wouldn't work.]

Do you guys have any idea what's the problem here? I wrote this because some other users were experiencing the same problem and maybe this can help figure out what the problem is. Oh I forgot: THIS HAPPENS ONLY IN THE DISCOVERY MOD: BOTH IN THE HOME SCREEN AND IN THE GAME. Single player campaign and other mods(crossfire) run fine.

Thanking you in advance for any assistance you can offer
DanielDarko