Today I was trying to get 64-bit Windows 7 onto a Dell Optiplex GX620 and needed the audio driver for it.  I found this page which pointed me at a Vista driver for the same sound card on Dell's FTP site (R145149.exe).  I downloaded this and let it extract to the default location but then canceled the installer.  From device manager I told Windows to look in C:\dell\drivers\R145149 and accepted one warning and now sound is working.  The original site also has instructions for the 32-bit version of Windows 7.