theres a few threads on this.
if you still have your old backups you can recover most of the site data.
if you are on windows, open the back up in winzip (file and open) and you will get a bunch of UNKNOWN files and a text file.
from what i can tell the text file has usernames, passwords and such for the domain. also looks to include database settings.
the unknowns are accually data. run WinRar and do file open and select one of the unknowns and you'll get another unknown. right click and view file. and you should either get some directories (like httpdocs) or a text file which should by the mysqldump.
I know you can do this from console as well but I don't know the commands off the top of my head.
and as a side note, a couple of my domains did not have the mysql dump but it did have the user/pass's.
I hope this helps
Joe