How Do You Get Deleted Videos Back From A Hard Disc Video Camera?

My mum just bought this new hard disk video camera, she took it to Tasmania with her and got videos of my family over there who we very rarely see. So they are pretty important to her.
I was just playing with it and I got this goofy video of myself so I went to delete it… When I deleted it I kind of deleted all of the others :O and I REALLY need them back.
If anyone knows any good programs I could use to get them back it would be much appreciated.
Thanks.