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>Will my VFP codes, forms and projects work into VFP 9.0
>environment without changes ?

Most likely moving from VFP6 to VFP9 will requre some tweaking of your code because a lot of stuff changed since then. I would recomend you to read What's NEW in VFP 7.0, 8.0 and 9.0:

- http://msdn.microsoft.com/library/default.asp?url=/library/en-us/fox7help/html/newWhats_New_in_Visual_FoxPro60.asp
- http://msdn.microsoft.com/vfoxpro/using/documentation/default.aspx?pull=/library/en-us/dv_foxhelp/html/fooriwhatsnewinvisualfoxpro80.asp
- http://msdn.microsoft.com/library/en-us/dv_foxhelp9/html/d18b257b-4e8c-4bd7-bc46-682526474e68.asp

In particular, pay attention to SET ENGINEBEHAVIOR and SET REPORTBEHAVIOR commands.