There are some mechanical repairs that can not be done easily by the average home mechanic, but there are some that can. My daughter's boyfriend recently got a used car that needs some work. Some of what it needs I know is beyond my husband's abilities as a weekend mechanic, but using sites like eHow help determine if it's possible or not.
As an example, their project -- changing the power steering pump is marked "moderately easy" -- this means they have a good chance of pulling it off and being able to save the boyfriend almost $200.00 depending on how much the tool rental is.
eHow also confirms for me that one of the other car repairs is not something they want to attempt -- replacing a tie rod since that is "moderately challenging."