Windows 7 is about $100 and Office 2010 is $200, total cost $300. An office worker making near minimum wage costs $10/h. If that office worker loses 30 hours of labor, it becomes worth while to buy the software. A reduction of productivity by just 2% over the course of a year amounts to 40 hours of labor lost.
A non-productive worker actually costs much more than their hourly wage though, benefits, employer taxes, facility costs also which roughly double that cost to $20/h. We can safely assume that it'll take a few hours to get acquainted with new software, after words your productivity returns to it's previous value, but if that learning curve costs just 2 work days they've come out behind with a cost of 20*8*2=$320.