Domains with a hyphen (-)

I've found a quite interesting keyword that has around half a million searches per month, according to Google Adwords keyword tool, but unfortunately the domain is already registered (even though it's parked. I've already sent an email to the owner).

However, the same domain with a hypen (only two keywords domain) is free.
How would this domain rank in Google?

Would it help achieving a good position for that keyword, even with the hyphen?

Thank you

If you get it with a hyphen, your wort competitor will be the guy who has it without one. Since he's doing nothing about it I think you don't have to worry about him either.

His domain was first registed on 1996, but currently is a parked page, and according to Google's cache, has been for a while.

I'm gonna go ahead and purchase the domain then!