In linux, punching in uptime provides you with how long the system was up without a reboot. But how to do this in Windows? There is no real indication to be found anywhere. Here's how.
The uptime can be found using the command prompt.
net statistics server
(and hit Enter).
Find the line that starts with Statistics since...: it will tell the time the server was up from.
Note that you could shorten the commands like so:
net stats srv
The above has been tested with: Windows 2000 (all versions), Windows XP (all versions), and Windows 2003 (all versions). It will probably work on Vista as well.
For other versions, use the tool and explanation from this article: http://support.microsoft.com/kb/232243.
This solution was found at http://support.microsoft.com/kb/555737.