How does Windows 7 detect my switches?
Solution 1:
I believe it uses the Link Layer Topology Discovery service built in to Windows 7. I believe you need another Windows Vista/7 machine with LLTD enabled on your network for it to work completely. It seems like you already do and that is how it finds your switch.
This Word Document goes into a lot of technical detail on how the discovery process works.
Solution 2:
Big brands in networking won't support LLTD on their devices. Windows on the other hand doesn't support LLDP so we seem to have a gap.