You'll hear over and over how the megaminx is "just like" or "very similar" to a 3x3x3. It's mostly true: It's quite similar. You can do F2L to solve several "layers" of the megaminx. The first set of F2L is sort of obvious: It's the first layer corners and the edges above them. The next set of F2L pairs are the corners and edges above the ones you just solved. It's a little hard to describe in words, but you can use F2L to solve the vast majority of the cube from here, being a little creative.
When it comes to the last layer, I had trouble. I was able to get it partially done using adapted algs from the 3x3x3, but I honestly couldn't get the whole way by myself. Maybe it's because I was doing it with a megaminx simulator (I don't have a real megaminx puzzle). Maybe I was too lazy.
Either way, I went looking for solutions and didn't find many that I liked. There are a few here on the wiki page:
http://www.speedsolving.com/wiki/index.php/Megaminx_Speedsolving_Methods
One of those might float your boat. If not, I found a very simple solution that I like quite a bit at the Meffert's site (google found it for me). It's here:
http://www.mefferts.com/puzzles/megasol1.html
You can use that as a complete solution, or do what I did, and use F2L to get all but the last layer, and then use the end of that solution to solve the LL.
Finally, the simulator I was using has two solutions, but they are mostly in words, as opposed to algs. They list a few algs, but not many:
http://virtualpolyhedra.googlepages.com/megaminx.html
I was able to get most of the way there with their words explanation, but I couldn't ever quite complete the last layer with their method.
I hope that helps.
Brian.
