Windows Uptime

Windows Uptime

What is the calculation for system uptime on a windows 2000 server machine
 
I am using SNMP .1.3.6.1.2.1.25.1.1.0
 

The value i get is 7/2/2009 5:09:38 PM (5 ms) : Value: 282812317
 
I want to know how to calculate it and display in readable terms

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