Press Record.

http://snipurl.com/alarmclock
"(IE Only) Set an alarm that will play any sound from your computer. You can even select a snooze time after it sounds" It works off your system clock. It works.
This alarm clock thinks its a web page. Silly.
If I was smarter
I would build this into a web page.
Surprising. After much googlery and backlink checking, i don't think anyone else has either