If your workstations are using the NTFS file system, you can use COMPACT.EXE that is included with Windows to compress files with a certain extension. For example, to compress all of the .CHM files (which are rarely used), use the command: COMPACT /C /S:C:\ *.CHM
Here is a list of all the available parameters:
COMPACT [/C | /U] [/S[:dir]] [/A] [/I] [/F] [/Q] [filename [...]]
Used without parameters, COMPACT displays the compression state of the current directory and any files it contains. You may use multiple filenames and wildcards. You must put spaces between multiple parameters.