>Hello, i'd like to know if i have installed VFP6 and then i install the VFP7, will have some kind of trouble between them.

Yes they can coexists if you don't share foxuser.dbf between them.

>
>what are the differences between VFP6 and VFP7?

Open help file and read "what's new" section.

>Should i change to VFP7?

I would recomend that you skip VFP7 and switched to VFP8.