Legong - do a search on QL for 'scuba' or 'diving', there have been several posts about diving in Qatar before.

taazzoo - That website doesn't appear to have been updated since December, which doesn't create a very good first impression really.

harsha - you can "go do for once for the fun of it" as a lot of scuba companies offer a "taster" course, where you can do an accompanied scuba dive with no previous experience.