There seems to be some .NET dependency but it's not specified. It runs fine for me in Vista64 and Windows Seven 32 bit command lines.
If you download the source it has a handy batch file you can use to convert subs in a folder to .srt. It supports quite a few text sub formats. The documentation is practically zero. Run with no args on command line to get help text.
It's for those occasions when you have more than a few subtitle files to process so that manually loading in a Gui and saving would be tedious.