Which Client OS do you use? Windows 2000, XP, Vista, Linux?
Is it a Workgroup installation or do you use Domain Login?
Have you patched the windows registry of the clients, which connect to the SME-Server?
Is the client slow even when working locally (while attached to the SME-Server)?
How do you attach to the SME-Server?
What about a Peer-to-Peer-Network under Windows? Is that slow, too?
How do you connect to the internet? What TCP/IP settings do you use? Who is DNS-server?