an ethernet switch which can handle 10BT and 100BT will take care of any ethernet speed changes required between computers and artnet boxes, or down any backbone link.

http://www.netgear.com/products/busi..._switch_sb.php

I run artnet at Gigibit ethernet or over airport to a switch.
it also runs over fibre.

only the connection between the artnet box and final switch needs to run at 10BT.


i dont know anything about specific protocol issues with grandma desks.


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for example you can use a g5 with gigabit ethernet turned on for say - file sharing - and use artnet at gigabit ethernet speeds down the same link - as long as you use an ethernet switch which will convert ethernet to 10BT to connect to the artnet box.
Ethernet switches will try to maintain the full speeds of all the connections. they have buffers.
they also have routing tables to route data only to devices that that are active down a link.