In regards to what tartan you are 'allowed' to wear, Brian Wilton, Director of the Scottish Tartan Authority has this to say:

"Often over the years one has heard people explaining they have a right or that they are entitled to wear this or that tartan...infact no such right, in any legal sense, exists for them or anyone else...the only considerations which govern the wearing of a particular set are usage and good taste."

Basically you can wear what tartan you like the look of! Of course looking for a tartan that matches a family name is a nice touch, but often names don't have a tartan. Look for Septs (Family of names) that your name could be associated too (An example is MacBain is part of the MacKay sept).

Hope this information helps, just make sure that you find a tartan that you like!

Stuart