If you are using 6i client-server forms&reports then this works happily with 10g. You do not need application server as long as TNS names is setup right.
I assume you are using the web forms. These need to be converted via 9i forms.
1) Convert the .FMBs to text format FMT using bin/ifcmp60 from 6i
2) Convert the FMTs back to FMBs using 9i bin/ifcmp90
3) Compile the FMBs to FMXs using 10g bin/frmcmp