well, never done this however knowing alittle bit about networking, I would presume that your PC or the folders that contain the music and video should be shared out so that the contents of the folder(s) would be made known to the network and to the xbox. The xbox probably does see the PC however is looking for contents of the PC and if the contents are not shared out, the xbox might not pick anything up. Never done this so I could be wrong here.
Your router should work well, however just FYI, v1.21NA was not a good release of FW for some people. If you see any internet hang or no internet and you have to reset the router, upgrade to v1.22NA, this fixed this issue. However keep what you got if it working.
I'm sure this is just a configuration problem. Maybe others have some more info about this as well. Let us know what you find. Would be helpful if we could document this for future users.