exchange server backup

Could any of you clever people out there please tell me the best way ( and which files ) to backup on exchange server 5.5.
Do I back up the whole of the exchange directory or just some of it. The other problem I have is
the disk that exchange is installed on is getting quite full and 1 folder ( the DSADATA one ) is full of EDB.Log files is it safe to delete all these files .
regards
Pete Sinclair