I have a mixed environment of Windows, Macs, Linux and BSD-UNIX so I understand the need for interconnection. It's easy when using standard protocols and services but ... Microsoft never plays nice.

You can connect from Mac OS X to Windows using Microsoft free Remote Desktop Connection for Mac. You can remote to a Mac from Windows using Virtual Network Computing (VNC). While Macs (and UNIX and Linux) support the standard VNC service out of the box, Windows does not. For Windows you will need to install a VNC client.

Links:
<a href="http://www.howtogeek.com/howto/windows/tabbed-rem..." target="_blank">http://www.howtogeek.com/howto/windows/tabbed-rem... - Tabbed VNC
http://www.howtogeek.com/howto/windows/tabbed-rem... - Tabbed VNC.
http://www.microsoft.com/mac/products/remote-desk... - RDP for Mac.