Ok for anybody encountering the same problem, the solution is to make a simpletext file and name it "Groove Agent location" (without " " )
On the first line enter the file path to your vst plugins folder using ":" as separator, like this:
Macintosh HD:Applications:Emagic:Logic 6 series:Vst plugins:Groove agent: (the last entry should be "Groove Agent:" - not "drummer.000")
Place this in prefs folder and you should be good to go.
(I copy/pasted the file path names from Sherlock to make sure of the correct characters/spellings...)