If you run the command prompt as administrator, then type "powercfg -h on" it should return Hibernate to your list of choices.     Tom XPS 420, Q6600, 4GB, 500 GB, Vista Home Premium XPS 420, Q6700, 4GB, 750GB x2 (RAID0) Vista x64 Ultimate XPS M1330, 2.4 GHz, 4GB, 320GB, Vista x64 Ultimate XPS M1330, 2.4 GHz, 4GB, 320GB, Quad Boot: XP Pro x64, Vista x64 Ultimate, Ubuntu, Media Direct 
I just recently upgraded my XPS M1530 to Vista 64-bit Ultimate and I no longer can go to hibernate mode I can only "sleep" or "shut down" is there a fix for this?   Thanks, Marcos
Vista 64-bit Ultimate upgrade