what? Is he an idiot?
What on hell has the audio conversion to do with the graphics card?
Couldn't he find anything better to tell you?
DDR 400MHz RAM is sure faster than the 333MHz but it doesn't such a difference. As for capacity you already have 1GB...although this is not also the problem.
I don't think the motherboard slowers this.
My opinion is that you haven't made all the appropriate adjustments in BIOS.
Do you have the latest drivers for your motherboard's chipset.
It is 100% a software or OS issue, not hardware...