There's a course on here called 3o minute backlinks, take a look for it and you'll have all the information you'll ever need. There is a free way of doing it, which takes time because it's manual and kind of limited.
The course I mentioned covers it in video and I think there's even a browser creator in the zip. Not sure if the creator works, I never used it. You can go to conduit.c0m and just make a toolbar on there for free.
However the method is basically you creating a piece of software - toolbar, browser, etc. something real simple that takes like 5 mins
You create a PAD file
Submit PAD file and your software to software directories within the PAD submitter. To get the 'unlimited' backlinks, the software generally runs about $99 starting and it all goes on autopilot pretty much.
Then just wait for the links to get picked up.
It's boring and not very exciting, but it's just one of those little things you do that add up over time.