I have looked at this thing a few times over, am 100% positive this dell keyboard doesn't have one.
You can customize what keys to use for SweetFX by going into the SweetFX files and open with Notepad the file
injector.ini.
Once the file is open, you'll see a few lines that look like this:
;toggle shader keycode
key_toggle = 145 ; 145 = the SCROLL_LOCK key
;make screenshot keycode
key_screenshot = 44 ; 44 = PRINTSCREEN
;reload shader files keycode
key_reload = 19 ; 19 = the PAUSE key
Those are the keyboard commands for enabling SweetFX, screenshots and reload shader files. To change the keyboard command, just edit the key toggle number. For example, if you wanted to change the keyboard command to enable SweetFX from the Scroll Lock key to the Home key, all you need to do is change the key_toggle number from 145 to 36. Once you make the change, it should then look like this:
;toggle shader keycode
key_toggle = 36 ; 36 = the HOME key
Once your done, just save the file and play.
For a complete list of the javascript keyboard command codes, go to this site:
http://www.cambiaresearch.com/articles/15/javascript-char-codes-key-codes.
ack-ack