I have a 2008 Server box that is running file sharing between 2 Apple G5's. When I try to upload a file say one that is 500 MB. The upload will start, immediately jump to about 60 megs, slows down on the transfer down to 0 for a few seconds, then picks back up to full transfer rate, then repeats the cycle for the rest of the transfer. Any ideas on what is wrong here?
Chances are good that the G5's and Server 2008's TCP stacks aren't able to stabilize the connection. This typically a tcp-windowing fault of some kind. Microsoft rewrote the Windows TCP/IP stack with Server 2008, and that has caused various issues with older TCP/IP stacks, such as with your G5's and whatever OSX version they're running. Laying blame is tricky here since there are many ways to build a TCP/IP stack.
You may be able to tell the Windows IP stack to behave differently enough that transfers are speedy. Unfortunately, I don't the exact magic sauce that'll make it work for 10.4 or 10.5.