I just purchased a home that was built in the 70's. The house has been vacant for awhile and someone has cut/stolen the copper pipes that bring water into the house through the hot water heater. How do fix this? (DIY of course) Can I use PVC?

You can use CPVC, the yellow stuff, for potable water but not plain PVC. That stuff is great for drains. Replacing with copper is probably going to require less transition couplings but also some soldering skills. Its pretty much up to you unless your city has codes againist CPVC.