One of the Joy`s of owning a Dell system, a GX 620 to be precise.
Far as i remember people had problems with finding a Vista driver let alone a windows 7 driver.
In fact if you go to the website drivers section of dell, I think they only supported up to windows xp x64. So no luck there.
But then again it is Dell, so there is no surprise!, since they like you to buy a new system from them at about a two year step is it.
There is one here, but it is a vista driver, you may have some luck, it may work but I doubt it. Give it a try anyway.
Vista audio driver for Dell GX 620.http://ftp.us.dell.com/audio/R145551.EXE