I had same problem when I switched from my Pen 4 to the new one I built a Quad 4. My brother did too when he switched from his Athalon to his new Quad he also built.
Same stats AC97 with Logitech speakers 5.1 and had at the time Vista hard drive and XP SP3 on another hard drive. Went from Audigy sound card on the P4 to AC97 internal MOBO sound on the Quad.
Found out on both the Vista 64 HD and the win XP32 HD had to first setup the devices in Windows audio in control panel and configure in DXDIAG on run command. Then restart and come back and install the AC97 drivers and Realtek platform for setting up speakers. Had to do each hard drive individually.
My brother had to do the same song and dance.
Strangely enough Win 98/2000 and DOS/WIN3.1 and Linux hard drives did not have a problem. Chalk it to Microsoft to make things difficult in the new instead of learning from the past.
Hope this helps......
Note: If you go to either your speeker manufacturer or REALTEK for help, your speaker Manufacturer will probably be more help.