as long as you have a reasonable grasp of basic engineering principles, D.I.Y is not a problem, just make sure you have good tools and good information before you start, and preferably somewhere warm clean and light to work, gravel drives at 11pm in the pitch black is never going to give good results
A lot of people try to make out building engines/ diy maintainence etc is a lot harder than it is, and in reality most jobs on a car are very very simple. I do a lot of D.I.Y work for myself and freinds, and the results are usually very good, and I get to save loads of cash and learn how my car works