I have made an HTML Application last year.
Check it out. You will also find several style sheets from GPX to KML, KML to GPX etc.
I have also an XSD schema there.
XSLT html application You will find some threads on this application as well
You can also send KML from a webpage using the Keyhole(GE) ActiveX API.
There is a thread on that aswell.
Good Luck
Cybarber