if it's a OEM Vista you have to deal with NCIX, if it's a retail box purchase after June 26 you look here
Windows: Windows 7 Upgrade Option
here a quote from Microsoft, so iI guess NCIX do not associate the cost to it.. :
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I bought a new PC with Windows Vista Home Premium in July 2009. Why don't I qualify for the Windows 7 Upgrade Option offer?
Participation in the Windows 7 Upgrade Option is decided by the PC manufacturers. There are costs associated with implementing the offers so they may opt out of the program for certain models, particular timeframes, or in specific markets. We encourage customers to work with their PC manufacturers to better understand availability.