Check these out..
ftp://www.detonation.org/pub/muddasheep/hqa_ost/
Note that they are on FTP, so dont panic if your browser takes a while to load the pages (It does for IE)
Try them out. They are really awesome, especially ambiance.
And who says that Austrians can't make music?
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(On, and check www.halfquake.com Version 1.1 is out)