[glc]

I wouldn't use USB - I'd use a PCI or PCI-E adapter with an external antenna on a cable.

EDIMAX EW-7128Gn PCI Wireless Adapter for PC and Mac - Newegg.com

Intel 2200BNHMWDTX1 PCI Express x1 Centrino Advanced-N 2200 for Desktop IEEE 802.11b/g/n Up to 300Mbps Wireless Data Rates - Newegg.com