How do you determine table structure using DTI?

I have a database with DDF files and am looking for a way to determine what

the table and index structures are by using the DTI.

The PvGetTable() function returns field info, but not the field offset and

the "flag" does not specify that fields are nullable so I can't find a way

to infer the field offsets.  Is there another function that I should use 
that can give me the field offsets and information about nullable fields?

Thanks
- Greg