What is the easiest way to do a remote login over a local network, ala Remote Desktop?
(preferably using something free)
RDP client for Mac
There is also CoRD which is an open source RDP Client for the Mac. I find the UI for managing sessions of the Microsoft client to be a little bizarre. CoRD is better in that respect.
All good options above, I just want to add Log Me In. Very easy to install and use - just create a free account, download, and run the installer. I hope this helps.
You can also use VNC. There's a plethora of servers and clients available for a multitude of platforms.
Another solution is (the Free for Personal Use) TeamViewer. This can work over LAN, as well as over the internets.
You can also set it up on Windows to run as a service.