Become a MacRumors Supporter for $50/year with no ads, ability to filter front page stories, and private forums.
Use the search function. You don;t even provide enough information of what you are going to install or use it for,
 
I'd put at least 30GB into. My reasoning is that whenever someone says, "I'm only using 1 app," is wrong. They tend to start filling things up.
 
You could install Vmware or Parallels for something like this.

That way your HD isn't mangled up and you can use some of the nifty snapshot utilities in case the VM gets borked.
 
Register on MacRumors! This sidebar will go away, and you'll see fewer ads.