Since the systems connect when booted to Windows 98, we know it's not a connectivity or hardware problem. Therefore, it must be a configuration problem. If they're able to connect while plugged into the Portland network, perhaps you need to change their IP address and default gateway configuration when plugged into the Seattle network. I wrote a book a few years back, NT Nework Plumbing, which has good information about troubleshooting network problems. The whole book provides important background information, but the most relevant chapter can be found online here: http://www.windowsitlibrary.com/Content/386/08/toc.html.
This was first published in December 2001