Are all Nikon lenses compatible with the D3100?

I know that the Canon T2i is compatible with all Canon lenses and I was wondering if the D3100 did the same with all Nikon lenses or if there are restrictions.

Depends on what you mean by "Compatible." The D3100 will take all AF-S and AF-I, Because they both have the built in autofocus motor built into the lens.
The older Nikon lens required the camera body to have the autofocus motor for it to work. The higher end models have them, but not the D3100.
So basically older lens will work on the D3100, but not the auto focus.

All AF-S Nikkors are designed to work with All Nikon dSLR's including the D3100.

There are still some legacy lenses that are available that are AF. Those older lenses must be manually focused when used on entry level Nikon dSLR cameras like your D3100

For clarity, here is a complete list of Nikon cameras and lenses and their compatibility.

http://www.kenrockwell.com/...y-lens.htm

NOTE: NO Canon lens made before 1988 are directly compatible with Canon EOS cameras

Yes and no. To start all canon lenses, made with the Fd mount will not work on a t2i so not all canon lenses work with the D3100. Almost all nikon lenses work with the D3100 but Af-d or older lenses won't autofocus.