Yes, you have to create an account with Xilinx.
Here is an overview of the tools available from Xilinx:
http://www.xilinx.com/support/download/index.htm
ModelSim XE is all the way at the bottom.
If you download and install it, I think there is an entry in the
(windows) start-menu item (for Modelsim) that helps you to obtain a
license file for the free version (I think it uses the MAC address of
your network card for that).
It also comes (or used to) with a licensing wizard to help you install
the license file you will get from Xilinx (by e-mail if I am not
mistaken).
I haven't used it for a while, so I hope this information is helpful
and not outdated.