virtualbox wont show USB ports in the guest OS

[Joep L. Blom]

I hesitate a little to ask this question as it is I think one of the 
most frequent problems with virtualbox. But the suggestions obtained 
from the vbox list didn't work.
The problem is that the way Ubuntu(9.04) handles USB-ports is mysterious 
to me and moreover, virtualbox apparently changed the handling of USB 
ports between version 2.2 (which works in Hardy on one system) and 
version 3.04.
I have the distinct feeling that the problem is in the permissions as I 
but I can't find out which are not set. I even tried to set the 
/proc/bus/usb directory chain to 777 (which is definitively NOT a good 
idea) but it didn't work.
Virtualbox starts up normally and the Devices tab shows the USB-ports 
but they are greyed out. In the vbox manager the USB ports are set. Also 
the local user - who starts virtualbox - is subscribed to the group 
vboxusers as recommended in the manual.
The manual also says that in 'modern hosts' (I have a brand new AMD 
Phantom  II system) that's all that's necessary to have the USB ports 
seen in the guest OS (in this case W XP).
I don't want to start virtual box from a root account.
Of course I can try VMWare but that's a hog and moreover not Opensource 
(I know the Sun version is also not but...).
At the moment I am out of ideas and maybe somebody of the guru's in this 
forum can shed some light on my problem.
Sorry for the long mail,
Joep