Cross-Platform development

hello,

i plan to convert a filemaker database to postgresql and need some
information before actually starting the conversion.

actual project:
relational database with appr. 40 tables for obstetric data (perinatal
statistics in germany, diagnosis- and operations-code-tables, user-data
...) developed over the last 4 years.
developed with filemaker-pro v5.0 to 6.03 on mac os, distributed to
hospitals running windows nt/ xp/ 2000 using filemaker server and
filemaker pro.

planned:
moving database to postgresql
development on macintosh with mac os x (darwin=bsd unix)
using java, jdbc, for portability perhaps swing as gui.

questions:
1) does anybody know if it is possible if there exists a gui-design
-software for mac os x and java so that i can develop the interface
completly on my mac and port it to windows.
2) are there better ways instead of using java/jdbc regarding
portability, requested time ((and speed))

thanks in advance

martin