We've published the following article on MSDN:
"Validating Form Fields Using JavaScript in FrontPage" at http://msdn.microsoft.com/office/default.aspx?pull=/library/en-us/odc_fp2003_ta/html/odc_fpValidatingFormControlsUsingJavaScript.asp.
FrontPoint blog Sitebuilder Blog (FrontPage MVP) Kathleen Anderson's blog (FrontPage MVP) John Durant's blog
Disclaimer: This posting is provided "AS IS" with no warranties, and confers no rights. Use of included script samples are subject to the general copyright terms.