TeamViewer allows you to connect remotely to a Windows 7 computer, Mac or Linux computer through the Internet and take control of the system for support and sharing.
Most important point is TeamViewer (both Windows 7 version and Mac version) is free for private users, it is operational immediately after downloading.
It requires no installation (in simple run mode, you can install it too) or disabling the firewall.
Of course, the application must be present on the two computers in any combination: Windows 7 and Mac, Windows 7 and another Windows 7 PC, Mac with another Mac, Mac and Linux computer, Linux computer with Windows 7 PC etc.
Team viewer website is self has screenshots and support section; so we are not elaborating the process.
Note: When you will surf from Mac, you will get the link to download for the Mac version of TeamViewer. TeamViewer does not work with Hackintosh.