Wow... this is getting a bit crazy following which thread to answer you in Grazie... coupled with my own (somewhat similar) question my brain is really having to work hard (must be that it is late here).
Anyway... my Graffiti FX appears in the Plug In Chooser (although I did not upgrade to 5.0b... due to fears about the various issues I heard about that version (MPEG templates).
When I installed the full version I was careful to re-direct the installation folder so that it went into the V5 folder rather than my V4 folder (which I still have installed on my system).
Is there some dll-file you can drag on top of the vegas window? Sometimes this works. A window will pop up that asks you if you want to "register" the plug as a plug-in in Vegas.