I'm gonna go with mark on this one. There's 2gb of ram and a speedy dual core processor, its not a RAM issue. It will be something related to the sound or video drivers/setup. Faulty ram will show itself in other areas of the laptops performance, not just a stuttering game. A load of system hogging processes will slow the laptop down in most games, not just one, it also wouldn't be only when there is sound going on... it'd be all the time.
He's mentioned there's issues with the sound and video drivers, yet you think its a ram problem and now you've had someone else (incorrectly) agree you think your definitely right and the more logical idea is wrong.
Keep at it with the sound and video drivers, download them a few times from different places and try running them in windows safe mode to install them. Try entering the laptop setup menu during the boot and disabling the sound chipset and letting it boot up, then restarting and enabling it again in the setup menu again. Try uninstalling drivers entirely then restarting and installing them again.
If that doesn't work and its vista try right clicking on the start icon on the start menu or desktop icon and running it as an administrator. Might not be the problem but sometimes fixes silly little issues like this.
EDIT: As a separate train of thought. If its a laptop with a decent spec but a low budget graphics solution such as this there could be a high chance that they tried to increase the graphics performance by allocating a certain amount of shared memory. This means your laptops graphics chipset will effectively use your main system RAM as its own, giving you either 1.75gb of ram or 1.5gb depending on how much it uses. With vista installed and a game with a recommended 2gb of ram for smooth play it might be just a little bit too much for it. If this is the case try bumping the resolution down in the games graphics settings, it'll need less memory and if it stops the jittering it might just be the cause of it.