An easy way to find out just how long that Windows server has been up:

Open a command prompt and type NET STATISTICS WORKSTATION and you'll get the following. The 'Statistics since xxx' shows when the machine was booted, along with a bunch of other good info. (Note you can also type NET STATISTICS SERVER, but the info it gives you is a bit lame)

Workstation Statistics for \\MACHINENAME

Statistics since 2/19/2006 6:38 PM

  Bytes received 187770141
  Server Message Blocks (SMBs) received 83361
  Bytes transmitted 44165182
  Server Message Blocks (SMBs) transmitted 83513
  Read operations 9122
  Write operations 2764
  Raw reads denied 0
  Raw writes denied 0

  Network errors 0
  Connections made 1647
  Reconnections made 0
  Server disconnects 7

  Sessions started 0
  Hung sessions 0
  Failed sessions 0
  Failed operations 0
  Use count 612
  Failed use count 2