Someone asked the question on the evolt mailing list about validating XHTML behind a firewall. The most popular way to validate XHTML is using the w3c HTML validator, however the only options are to enter a url, or to upload a file. That can be cumbersome, so steve clay wrote a handy php script that crawls a url and uploads the file then displays the results. I ported his script to ColdFusion below. It works great in CFMX, but there are issues in CF5 (cfhttp is url encoding the charset). You might also want to wrap a html tags around this code.
<!---
Ported To ColdFusion by Pete Freitag www.cfdev.com
Based on http://mrclay.org/junk/software/private_validator
License: (GPL) http://www.opensource.org/licenses/gpl-license.html
--->
<cfoutput>
<form action="#CGI.SCRIPT_NAME#" method="post">
<label for="location">Validate Local URL:</label>
<input type="text" name="location" value="http://#CGI.SERVER_NAME#/" />
<input type="submit" value="Validate" />
</form>
</cfoutput>
<cfif IsDefined("form.location")>
<cfset tempFile = GetTempFile(GetTempDirectory(), "validatorFile")>
<cfhttp url="#form.location#" method="get" path="#GetTempDirectory()#"
file="#GetFileFromPath(tempFile)#" />
<cfhttp url="http://validator.w3.org/check" method="post" resolveurl="yes">
<cfhttpparam type="formfield" name="charset" value="UTF-8">
<cfhttpparam type="formfield" name="doctype" value="Inline">
<cfhttpparam type="formfield" name="ss" value="1">
<cfhttpparam type="formfield" name="verbose" value="1">
<cfhttpparam type="file" file="#tempFile#" name="uploaded_file">
</cfhttp>
<cffile action="delete" file="#tempFile#">
<cfoutput>#CFHTTP.FileContent#</cfoutput>
</cfif>