My suggestion; not sure if it will work but you can give it a shot..
In your "HKCU\ControlPanel\Notifications\Random Numbers\" (the entry for your "Messaging: New text message")
Add a new string value named "Script" (no quotes, obviously)
And give it value of "v0pf0" According to the code above, that should make it vibrate continuously, play the ringtone, then flash LED indefinitely...
Like I said, dunno if that'd work. I'm still trying to iron some stuff out on my PPC or I'd try it.. just at a point right now I don't wanna have to flash to fix something I broke
Lemme know!
***EDIT***
I'm now doubting this for one reason:
The key for new email messages doesn't have a script key, and it by default does what you want, sound, vibrate, LED, but no screen activation.. HMMM..