Pad, try this link and install these drivers if you are on x86.... also supposed to work with x64, but I have only had it working/tested with x86, until now...
but i had the same problem after I installed 7. It worked fine at first, went to updates and got the problem. Used these drivers in the link and got it working again. My dummy self of course updated some MS (office and win defender) last night only to find that my audio had failed on me again.
Here's the link: Realtek
also what motherboard do you have (chipset)? and what platform of win7 are you running?