Virtual Wi-Fi (at Microsoft Research)

Connecting your computer to more than one wireless network simultaneously sounds like a multitasker's dream. You could install more than one Wi-Fi network adapter in your computer to do it, although this can be expensive and may not work the way you want for various technical reasons.

Microsoft Research has a different idea they call Virtual Wi-Fi. It allows you to have one physical Wi-Fi adapter connect to more than one wireless network. [Note: The free trial download for Microsoft Virtual Wi-Fi is no longer available.]

→ More - MultiNet: Connecting to Multiple IEEE 802.11 Networks Using a Single Wireless Card (research.microsoft.com)