Do you have a better way to browse Windows 7 machines in Finder (SL 10.6.5)?
Windows 7 has extra network security options, and one of them sets its discoverability. By default in Windows 7, when you connect to a new network you are prompted for what type of network it should be: Public, Work, or Home. These profiles set up the firewall and security options when on that network; I can't off the top of my head list all the things they specifically set up, but when you select Public, sharing and discoverability are locked tight, whereas in Home they are more relaxed.

It's very likely that you have set your network type to Public on your Windows 7 computer. If you open the Network and Sharing Center, under the name of your active network it should say either "Home network", "Work network" or "Public network". If it is indeed set to Public (or Work), click it and then click Home network. You shouldn't have any problems after that.

Alternatively, you can open the start menu and type Network and hit enter. This opens the Network window, which lets you browse other computers on your network. As soon as the window opens, a yellow bar should appear at the top informing you that network discoverability is turned off; click the bar and then click one of the resolution options. This may fix the problem as well.

I haven't had any problem in OS X connecting to my Windows 7 computers that are set to Home network, as they should be. But a Windows 7 computer set to Public network should be basically undetectable.