how do you remote desktop to mac osx from windows?

Use VNC. On the Mac enable VNC access in System Preferences => Sharing => Screen Sharing. On the PC you need to install a VNC client such as RealVNC.

Another option: TeamViewer

Simple download and run for client, no installation needed for impromptu help sessions... (Still, you can install if you want to).

Works well enough, and is free for non-commercial use.

As far as a cross platform solution PC -> Mac, VNC is the best solution. The slowness is likely due to a combination of the speed of your Internet connection, the resolution on your Mac, and the color depth you've chosen on your Mac.

See How do I… Connect Microsoft Windows systems to a Macintosh network?