From:
http://ppcgeeks.com/wm5-registry-hac...tion-t113.html
From the information below, it looks like you'll want to change the key value to vN, where N is the number of seconds you want the phone to vibrate.
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Change ringtone/vibrate/LED flash characteristics
If you would like more control over how your device rings/vibrates/flashes its LEDs on events, you can can change the Script values of these events. For example, for an incoming call performing 'activate device, play ringtone, wait 3 seconds, repeat':
HKCU\ControlPanel\Sounds\RingTone0\Script = "apw3r" (REG_SZ string, no quotes)
For performing 'active device, set volume to 33%, play ringtone, set volume to 67%, play ringtone, set volume to 100%, play ringtone (no repeat)':
HKCU\ControlPanel\Sounds\RingTone0\Script = "ac33pc67pc100p" (REG_SZ string, no quotes)
The following are the full codes available to you. Please note that all the codes are executed simultaneously except after a ringtone play / wait code. E.g. 'v1p' will vibrate and play at the same time, while vibrating for 1 second. But 'pv1' will play the ringtone through all the way first, then start vibrating for 1 second.
a = activate device
cN = set volume to N in percentage max volume
fN = flash notification LED for N seconds
p = play ringtone. Note that this will play the ringtone all the way through before continuing with the next code.
r = repeat. Note that this should be the last code in your Script string, if used at all.
vN = vibrate for N seconds
wN = wait for N seconds. Note that the device will wait this long before continuing with the next code.