Euded, no matter wich version of plesk you are running, download it, install it following the instructions on screen, change the group for the urchin user to the psaserv one, that will let you read the logfiles and procces it into urchin.
go to the forums on sw-soft.com plesk 7, third party software, search posts by me, there should be one thread from start to end on how to do it!
I did it some months ago and urchin is running on my server smoothly
best regards,