MSI P55A-G55 Starcraft 2 stuttering

Hi, I recently built and I have some stutter issues when playing games, which my local retailer thinks are caused by my MIS P55A-G55 motherboard.

Starcraft 2 has the most stutter. For example, when i make my first SCV or place my first barracks, the game freezes for about 2 seconds. It subsequently freezes on each new type of building or unit getting out.

It used to have stutter only in mid-game, but I recently updated my sound drivers because I had to reconnect the mic and run a test hardware each time i restarted the computer. The realtek up to date drivers fixed the mic problem, but brought in more stuttering. This led me to think it was caused by onboard sound. I used to think it was a video card issue and I already tried another brand and the problem still persists.

Tech support at MSI suggested it was caused by poor Windows XP driver support and that I should upgrade to Windows 7.

Do you think this is possible ?

Thanks.

P55A-G55 bios 1.0
Intel Core i7-860
Kingston ValueRam 4Gb 1333Mhz
Asus ENGTX 460 DirectCU TOP (the overclocked version)
Sirtec High Power 750W PSU
WD Caviar 320GB HD
Windows XP Pro SP2