Click here for the ModelSim installation instructions. We recommend you install ModelSim before Xilinx, so the Xilinx installer can pick up the ModelSim path during library installation.
Click here for the Xilinx installation instructions.
The SciTE text editor has a small footprint and has (arguably) a better interface than the ModelSim embedded editor. You can download a customized version of it here:
It's probably best to unzip it to your network share so you can use it from any computer in the lab.
Other text editors with good Verilog support: