in my personal experiance its almost impossible to get any uptime on a windows machine above 47 days ..... MS releases to many damn updates the require reboot. minus that instance my pc would be up from the moment i first installed XP pro till this very second that is the only time it has ever benn rebooted since then.
XP was installed 31wks 1day 8hrs 14mins 1sec ago
thats when i built this system