Problems with usb devices being "grayed out" is very common with virtualbox.
And it is almost always solved by editing the /etc/fstab file.
Follow these steps:
1.Open The Pclos Control center
Click "System" then "Manage users on system" then click the tab for Groups.
2.There should be a group called vboxusers, if there isn't one then create it.
3.Make sure that you are one of the members of the group called vboxusers, if you are not a member then add yourself by right clicking
the group, selecting "edit", clicking the tab "Group Users", and then putting a check mark next to your username
4.In the column labled "Group ID" there is a number assigned to the "vboxusers" group, remember this number. In my case the number is 501
5.Now (as root) open up your /etc/fstab file and add the following new line:
none /proc/bus/usb usbfs auto,busgid=xxx,busmode=0775,devgid=xxx,devmode=664 0 0
Be sure to replace "xxx" in the code above with the number that you saw during step4.
So in my case it would be:
none /proc/bus/usb usbfs auto,busgid=501,busmode=0775,devgid=501,devmode=664 0 0
6. Now save the file and either Restart your computer or do "mount -o remount /proc/bus/usb" as root in the terminal.