System volume information

Hello,
i m using windows xp as well as windows 7....recently i took an external hdd maxtor basics...i just tried how to use bitlocker.i tried to use it and after some time as i saw it would take much of my time i decided to cancel it hence i went to help and support in windows and saw how to stop from encrypting and finally decrypted the data...but now i have only 19 gb free space showing up as in display of the total 488 gb..i used only 388..i searched and searched and finalluy using tuneup..i came to know there was a folder inside with a name SYSTEM VOLUME INFORMATION.it consiss of 100gb....it s showing it consists of a file100gb..i tried and tried opening the folder and deleting many files...i was successful in deleting few filed but i could not delete the 100gb file as everytime i try to delete its saying see that u r not using the file or the file is not write-protected..kindly see that i can eliminate the file because i cant delete a single file in that and i cant format very valuable information present...would be pleased if u provide me ur valuable information..