<font color=blue>What kind of network are you refering to?<font color=black>
Our network is a Windows 2000 Server network with one fileserver which is the domain controller. Only 10 or so client computers. There is another W2K server machine in the domain which only acts as a mail/fax server. Both of these servers are Pentium 3 - 600 to 800 mhz machines (Dell Poweredge 2400).
I hired 2 different consultants that could only throw up their hands. One of them later advised me that he has gone back to previous installations of his and found that, indeed, the XP clients are slow, but there had not been anything to compare them to and so his client had not complained. Whereas, I was replacing 4 year old P2-333s with Windows 98 and the old ones were MUCH faster on the network than the new P4-1.8s were. With W2K professional, the new ones are very fast.
Two examples. Loading our tax preparation software - about 200MB from a CD - the update would take about 15 minutes on the old Win 98 machines. On the new XP machine I terminated the install at 45 minutes twice. Don't know when it would have finished.
Copying files from server to client. The old 98 machines took about 25% as much time as the XP machines.