See #6 here, if they also set a firmware password then your screwed.
Step by Step to fix your Mac
You'll need the 13" Early 2011 MacBook Pro machine specific 10.6 install disks, call Apple via phone to order if you don't have them.
You CAN'T use the 10.6.3 white retail disks which are cheaper, so don't let Apple send you those, they won't work.
10.6.8 will SCREAM on that machine, it's the last model catagory that can run 10.6.
I have the 17" MBP Early 2011, and using Firefox with the "make Firefox 10x faster" broadband tweaks.
Very fast and highly responsive machine, web pages load in about 1-1.5 seconds complete on 25 mp/s down on WPA2(AES) 5,400 RPM drive.
Also it runs the older PPC software/hardware drivers using Rosetta, which there are no longer any newer Intel versions, like Scrabble for instance or printer/scanner drivers. 10.7-10.8 doesn't have Rosetta.
Apple is supporting 10.6 with security updates as over 50% of it's users are on 10.6 because of software reasons.
Your machine is the 13" model, all integrated Intel 3000 graphics, so since 10.8 is a graphics hog, your video performance should be best on 10.6.
10.7 and 10.8 are better suited to SSD's as the boot drive (also Recovery HD hassles), because it gives better performance than hard drives.