To do this generally is dangerous as has been mentioned elsewhere.
However, it should be possible to have Mosaic only execute a program
link (whether it is a form ACTION or an HREF) if:
1. The page with the link is a local page (since remote pages shouldn't
point to local executables)
2. The program to be executed is local
3. The program to be executed is in your PATH (since PATH contains programs
you already trust).
In order to tell Mosaic to execute the link instead of reading the file,
an extension could be used (e.g., ".cgi") or possibly a different URL
form could be used (e.g., "exec://localhost/~dheiland/bin/anything"). Some
further distinction may need to be made between those programs that return
HTML (such as a local WAIS search on your private files) and those that don't
(such as click here to run xclock).