Using one of the following commands one can tell the uptime on windows i.e. the time since the last reboot occurred.
REM on WinXP
C:> net statistics workstation | find /I “Statistics since”
Statistics since 12/28/2008 10:35 AM
REM on WinXP, Windows 2000
C:\>systeminfo | find /I “System Up Time”
System Up Time: 1 Days, 14 Hours, 18 Minutes, 51 Seconds
An Oracle Spin by Alex Lima 
You can also download PStools, from http://technet.microsoft.com/en-us/sysinternals/bb896649.aspx which contains the command “Uptime”,\Pstools>uptime
has been up for: 1 day(s), 20 hour(s), 17 minute(s), 37 second(s)