For example, I had a Sound Blaster Live! PCI sound card, which is unsupported in Windows 7. No drivers, no sound, lots of problems, not resolvable!
Um, I hate to break it to you, but creative offers vista / win 7 drivers for that card on their site. We have lots of Opti 280's with that card at work, and have rolled the Win 7 driver into our image.