Install the latest version of .net on your machine. First notice that the download is HUGE, then go to windows\microsoft.net\framework and notice there will be a folder for every “final” version (1.x, 2.x and 3.x) in there. .net supports previous versions by INCLUDING them, 1.1 code runs against 1.1, 3.5 supports it by including 1.1 in the install.
159MB for versions 1.0.3705, 1.1.4332 2.0.50727, v3.0 and v3.5
It works nearly perfectly for backwards compatibility and really doesn’t take up that much disk space.
Most every other application on my system takes up more space than that.