i'd restart the install. it should be more than 1/3 done after 20 minutes. it maaayyyybe took that long for me to install the entire game. it should definitely be making noticable progress...if it's not, somethings wrong and i suggest starting over.
ctrl+alt+delete and look at performance, see if your cpu is being utilized. also check applications in there and make sure it doesnt say "not responding" by COD4