There's no problem installing as many different OS's as you want on the same hard drive [I use a 1TB drive with 8 choices; but have another system with 16 boot choices on a 500GB drive (mostly older OS's and a couple Linux installs).
However -- it's best to install them in a manner that they're completely hidden from each other, so there can be no interaction between the different OS's. To do this, I use Boot-It NG, which is not only an excellent boot manager, but also a superb image/restore utility -- I use it to keep images of all my installs; can easily restore from any image; and can easily add/remove any OS I want to try or no longer need.
See my comments here for a bit more detail and a look at my current boot menu:
http://www.experts-exchange.com/OS/Microsoft_Operating_Systems/Windows/Windows_7/Q_25014408.html#26159903