Photoshop :: Using CS5 On Bootcamp

I have Photoshop CS5 installed on my OSX. I'm planning to install windows 7 via bootcamp.  I read a long time ago there was a way I can get a windows key for my same program for a reduced price?  Or am I mistaken? I can't remember where I read it. I think it was buried in a forum somewhere and not among the top posts.  I don't know what validity it had.
 
That said, do I have to buy a whole another copy to use on the windows partition?  I hope not. It would be nice to be able to run photoshop on both partitions without too much extra cost. But if it costs a whole new copy of photoshop I'll have to accept having to reboot my computer between using photoshop and the windows programs I am editing for.
 
I had to edit this. Parallels is something I really want to use. I keep getting those mixed up.  Right now the cost is out of my budget, but parallels is another alternative I am hoping for in the long run and saving up for. I'm thinking of getting it in a few months.  I still wish there can be a more streamlined way I can transfer graphic files between both partitions without having to jump through a lot of hoops.