Can someone please tell me how to write a script that will search a text field for spaces and replace them with dashes?

If you really needs a script:

Set Field [ YourTable::YourField ; Substitute ( YourTable::YourField ; " " ; "-" ) ]

but that can be made using a calculation field or the option of auto-enter a calc for that field.

Place cursor in field (back up file first) and select Replace Field Contents and specify by calculation. Calculation would be:

Substitute ( yourField ; " " ; "-" )

If on-going, it can be scripted but I might suggest that you instead use auto-enter (by calculation) and uncheck 'do not replace existing value.' This would run every time the User leaves the field.

Thank you both so much! Was not aware of the substitute function.