Network Slow When Plugged in Switch

I have a network like:

config 1:
(dsl cable) - (linksys router 1 port) - (linksys switch - 8 port) - ( 3
win machines, 1 rh 8.0- machine)

config 2:
(dsl cable) - (linksys router 1 port) - (1 rh 8.0- machine)

When using the rh 8.0 machine in config 1 above it runs slow through the
mozilla browser.

When using the rh 8.0 machine is config 2 above it runs great through
the mozilla browser.

Do all the machines connected in config 1 each need to be running at the
same speed and duplex mode?

Mike