I experienced the same thing a while ago when I upgraded an office from an old 10bT hub to a 100bT switch. What should be been quite an improvement would slowly bring the network to a crawl. (WIth three computers, nothing major) I tried returning the linksys switch for a new one, and it did the exact same thing. Chaning to a different brand fixed the problem. I never figured out what it was that caused the slow down, but once the problem was solved I moved on and didn't worry about it.

Matthew