Hmmm... I can't understand what's the relation between your Windows 7 installation into a 200 GB. partition and your on-board sound problem.
By the way, I don't like big partition for OS. In all my PCs I've a partition of 40 GB. at the start of the disk drive just for Windows 7 and some programs, so I can avoid some disk fragmentation's slowdowns, also having less to defrag when I have to. PS
: What's the brand and model of your on-board sound or motherboard?