It looks as if you've not successfully installed the driver for the new sound card. I'm not sure why attempting to install a new driver should give you a message telling you that the files are in use by another program but the obvious thing to do would seem to be to shut down all other programs before trying again to load the driver file. When I refer to closing all other programs, I don't just mean the visible ones. You need to close the background programs down as well:
Press Ctrl-Alt-Delete and, one by one, close every program except Explorer and Systray. (If you're using XP, you'll have to go into Task Manager first). When you've got no unnecessary programs running try loading the driver from the CD again. Then reboot. And when you've finally got it working get a decent media player! Just about anything's better than Windows Media Player but VLC is wonderful (and free!):
http://www.videolan.org/
Chris