usb not working in virtual box

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http://www.linuxquestions.org – I have installed linux 14 nadia as my host os,and installed virtual box version 4.1.18-1 to run windows xp on it.All is fine but xp is unable to attach usb devices. I have created vboxusers by terminal command but no use.Please reply a step by step easy procedure to save me..........Thank u so much//////// (HowTos)