Useful free software for Windows  

MiKTeX Project Page LaTex for Windows, it also comes with a dvi viewer
The VIM Home Page vi editor for Windows
Ghostscript, Ghostview and GSview postscript viewer, it will let you print on a "non-postscript" printer. To install: download gs503ini.zip, gs503w32.zip, gs503fn1.zip (503 means version 5.03) and gsv23w32.zip (23 means version 2.3) to the same directory, unzip gsv23w32.zip and double click setup.exe. To print, pick the device corresponding to your printer in the print screen, if your printer is not on the list, use mswinpr2. (It is explained in the help file.)
Unix for Windows (U/WIN) U/WIN is a collection of commands, libraries, and header files that provides a UNIX-like environment for Windows NT and Windows 95. Work best for NT, so I haven't tried it myself.
Mathview Plugin The MathView Internet plug-in is available for Windows and Macintosh.