I\'ve installed parallels desktop on my MacBook to be able to run Visual Studio 2008 in a XP installation. Everything works great except when I decided to put my websites in
Or use SVN to hold copies in both machines and do commit/update as appropriate. That way you get versioning, history and if your project grows bigger, you can share with other devs.
I know dropbox also has history and sharing, but not check in/check out/conflicts and all the other advantages of a real source control.
Oh, if you have money you can also go for TFS. I would but it is just too expensive :)