Retro game controller and the PC

I’m trying to get an old Mega Drive gamepad (3 buttons) hooked up to the PC.
Playing some of the 4k entries from this year and also working on my own has made me realise that some basic java games would ‘feel’ a lot better if an old controller could be used.
I understand this may be take a bit of work and probably outside the scope of any 4k game!, but i’m confident this is possible!

Thus far:

1 x Mega Drive Game pad (9 pin DB9 plug)
1 x 9 pin serial to USB adapter
Adapter drivers
Java Joystick code from SourceForge: http://sourceforge.net/projects/javajoystick/

I’ve tried using the DirectPad and NTPad drivers for XP but these seem to be built mainly for Playstation or dreamcast controllers, and although windows recognises the adapter it won’t let me set up a 2 axis, 3 button game controller in windows without complaining that “something isn’t set up right.”
Does anyone have any advice for getting this working?

Cheers