Generally speaking, we look for people who are good at what they do (ie,programming or art) and have some combination of educational background and work experience, along with examples of work they've done in gaming. So, not only do we want good programmers or artists, but we want good programmers or artists who have examples of mods or plugins or game-related things they've done on their own that show us they "get" what it is we do here.
There's no magic degree, or school, or number of years of experience that we're necessarily looking for or need. The requirements for each job we're currently hiring for will give you an idea on a position-by-position basis the Jobs section of
Bethesda Softworks
Hope this information is helpful.