Can a osdx file be built for Sharepoint Services 3 to allow it to be included in Windows 7 Federated Search? I see stuff for MOSS 2007, but I can't seem to get it to work for Sharepoint 3.
Unfortunately, I think WSS doesn't have an RSS feed for search results - which means it isn't usable as a Win7 Federated Search source.
If your WSS environment is single-server, you could upgrade for free to Search Server 2008 Express and gain this functionality (and a lot of other cool stuff).
If you have a multi-server WSS farm, then I don't think it is possible without paying to upgrade to MOSS or Search Server 2008