Chevy Cavalier, water in oil. Is it possible for me to fix this myself?

Single mom, unemployed. and work on my car if people tell me how to do it. Just fixed a hole in Transmission pan, now need to tear down motor and see if it is head gasket or crack. Overhead cam is what scares me. can I do this? Anything special I may need? Will I ruin it? So afraid, never dealt with Overhead cam. (2.4)1996. How long will this take? The overhead cam is my biggest concern. I have done this before on a 73 Jeep, but not a newer car.