youve probably already done this, but just incase you havent, check that your sound card is recognised in your Device Manager.. you never know.
if its all connected properly and you can see it their, id try a clean re-install of the sound card driver and then Windows if needed.. also, is it a pre-vista sound card?
im just about to go gove Vista 64 a bash, im hoping i will be back online soon!
edit: i meant to say, no real tweaks in Windows that i know of.. i mean i use Auslogics to clean my PC and it has a 'windows tweak' program, but its stuff thats already blatantly their... but its handy because you can customize everything about windows from one panel.. but Auslogics is amazing because of its de-frag rather than its windows tweaks i suppose.
but UAC though, it can be soooo annoying.. .. it was blocking 2 programs at windows startup... windows advises in their help section, that if a program is blocked and you completely trust it you can click 'aways allow' or something, but when tis blocked the only options are 'allow' or 'block' (and clicking 'allow' only allows it for this session) and even when you go into the program thats blocking them you cant even enable them, it just tells you its not trusted!