have you checked if the IP of each machine isn't manually set. and that is conflicting with the IP of the other machines???

you can manualy set each machines IP

here is a example, say you have 5 computers and don't want them to conflict with each other , i am going to use 192.168.0.x as a example IP

1. set machine 1 to 192.168.0.2

2. set machine 2 to 192.168.0.3

3. set machine 3 to 192.168.0.4

4. set machine 4 to 192.168.0.5

5. set machine 5 to 192.168.0.6

i have always found out that if you set each machines IP address manually you wont run into any IP collisions my router is a 10/100 ethernet router with wifi G+ and i have my DA G4 (wired), my Beige G3 AIO (wired and wireless), my Yikes G4 (wired), my P 475 (wired), my friends PC (wired), my P1 windows 98SE PC (wired), my newton MP 2100 (wireless), and my xbox (wired). and i have each IP manually set ( in OS X or OS 9 use DHCP with manual IP)

even tho my Beige G3 has a 10 baseT half duplex ethernet it still will play nice with the other machines, even tho most of them connect at 100 baseT (as shown in OS X network pref panel) on each system but the Beige G3 still uses 10 baseT half and all the systems still connect fine with no IP collisions.

all of these machines can be running with no issue what so ever with the network.

i hope i didn't tell you something you already know, tell me how it goes. the collision's i think you are talking about are IP collisions, where 2 or more machines can be set to use the same ip. do what i said above to eliminate that possibility.