Using a serial to USB adaptor - Connecting simple serial FMS i/f to USB

[cometravi]

Hi,
I have been browsing this forum for quite a while and after some research decided to use an old serial to USB adapter i happen to have and build a simple serial interface (Mike's design i think) for a Futaba, and thus use the USB port on a winXP system to control FMS. (My laptop is one of the new beasts and does not have a serial port!!!)
I know there are numerous mentions of how an IRQ interface will not work with winXP and why a PIC interface is necessary, but i figured that this serial to USB adaptor was build 4 years ago when win 2K and XP were not even around and I have successfully used this adaptor on my win Xp system to syncronise my old Palm Vx palmtop.
So i built the interface to give it a shot but unfortunately it didnt work. Voltages were fine etc etc.
Any ideas on what might have gone wrong?
???