Are these computer parts compatible? (2)?

If your motherboard and CPU cooler are both Socket 775, you should be good to go. One suggestion, either wait for Windows 7 to come out, or use Windows XP. Don't waste money on top of the line parts if your gonna slow the whole thing down with a garbage OS. Also if you want to knock off some money, shop around. If you have your heart set on a prime gaming PC, then downgrading parts would defeat the purpose, but there's no reason you can't save some money by comparing prices on different sites like Newegg.com or Geeks.com. You could also check Xoxide.com for the case. As for the sound card it will work as long as you have the correct slot (PCI, PCIe, Etc.) available. You may need to go into the BIOS after installing it and disable the onboard sound, but it will work.