Network help!!

[ehunt32]

I work at a place where we give 90mins internet time for our users. If someone signs out one of our notebooks to use on the wireless network and we scan the bar code number in(its there membership barcode) and set the notebook for 90 mins when there done they return it. But that same person can go down to our desktop hardwire computers and use there barcode number and password to logon and get another 90 mins ...How can I fix this.

Thanks
ehunt