Missing Hard Drive Space

Hey guys!!! I have just transfered most of the music and other such files off my macbook to a hard drive. The problem i encounter is, that when i run a disk usage check it says i am using around 50 gigs, but when i check my remaining disk space it is somewhere around 160. My macbook has a diskspace of 250. The question then is, where has my forty gigs gone??? Any help with this would be much appreciated!!!

Regards
Mark

assuming that you have lion. thats probably the awnser lion safes a bunch of stuff over and over and slowly takes over your hard drive space i dont remember what the fix is for it but i know i read it on hear before check the OSX side of the forums. ( if you have lion) if not! there is the mac disk clean up app that shows you were all your space is going and what not! awesome tool!