Have you tried the following?
if you .chm is available at:
http://yourserver/yourfile.chm
then, you may be able to open it by:
- <script>
-
window.open('http://yourserver/yourfile.chm')
-
</script>
If you want this to happen on server-side, then you can have the above code spit-out by server code (RegisterClientScript).
Hope that helps.