FS9 aircraft cannot be converted to FSX format. However, FSX jetways should operate with FS9 aircraft.
The correct operation of a jetway depends on certain settings in the aircraft.cfg file. I know the matter has been diecussed on fsDeveloper. If you do a search on fsDeveloper for "Jetway", you should find it. Otherwise, a post in the aircraft design forum may help.
As Don said I think it is mainly a cfg setting to get the jetways working. The locations of the doors must be defined. There is nothing in the mdl for it.
With a future update of modelconverterx I hope to allow conversion of ai aircraft from fs2004 to fsx mdl format, since it can give some performance improvements to use fsx materials. But at the moment I am not aware of a tool that can do this.