Using virtualbox to mount a USB Drive

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I'm running CentOS 5.3 as my host OS, running XP as a VM. I added the USB drive as a filter in VirtualBox, however the USB drive dosent get recognized in the XP VM. Any ideas as to what I might be missing? My workaround for now is to share the folder, then access the share from Windows, but I'd rather just access the USB directly.