Check out this Group Policy setting in XP.
Start > Run > gpedit.msc
The navigate to
Computer Configuration > Administrative Templates > Windows Components > Terminal Services
With Terminal Services highlighted on the left, there will be a list on the right. (clicking on "standard" makes it easier to see) Double click on "Keep-alive connections" and look at the Explain tab. I think enabling this will solve your problem.
From the explain tab
"After a terminal server client loses the connection to a terminal server, the session on the terminal server might remain active instead of changing to a disconnected state, even if the client is physically disconnected from the terminal server. If the client logs on to the same terminal server again, a new session might be established (if Terminal Services is configured to allow multiple sessions), and the original session might still be active. "
Set it to something like 5 minutes
