I noticed that both the version 10 and version 11 files both use .fp7 files.

Where previous versions may have been .fp5 etc.

If i was to upgrade to v11 on one PC on a network, but keep the others on v10, would that pose a problem?

Does an existing file need to be converted for use with v11 from v10, or does it not matter if some PC have v10 or and others V11 when using the same DB file?

I noticed that both the version 10 and version 11 files both use .fp7 files.

Where previous versions may have been .fp5 etc.

Those previous versions using .fp5 would be version 5, 5.5, and 6. FileMaker has been using .fp7 for versions 7, 8, 8.5, 9, 10, and 11.

If i was to upgrade to v11 on one PC on a network, but keep the others on v10, would that pose a problem?

No problem.

The only issue would be if your version 11 user is a database administrator and modified the structure of the database file to add version 11-specific features. If all you are doing is normal data entry, then no worries.

Does an existing file need to be converted for use with v11 from v10, or does it not matter if some PC have v10 or and others V11 when using the same DB file?

No conversion is required. They both use the same file format.

Cheers

An added benefit of having any version 7-10 and also 11 is that two versions can be open at once independently, i.e. vs. 10 and vs. 11.