QUOTE
is there any adapter I could use to get the xbox into the sound card's headphone jack or any other port on my computer
If your sound card has an SPDIF-in port, you can route the digital audio out of the xbox there.
Of course you will need the appropriate cabling.
1. If the sound card has optical-in, use the optical audio out of the xbox.
2. If the sound card has mini jack or RCA SPDIF-in, you will need to make an optical to electrical converter. (either externally, or mod your box to have coaxial digital audio out).
For the second half of your question, you really need to be more specific (what type of cable adapter you mean). Generally you can display the video of the xbox on a PC monitor, either with a VGA adapter (which I assume you don't have) or if your computer has some sort of video-in port (usually composite)