The printer driver is looking for a parallel port - so something about the driver/software for the conversion cable should tell the driver VIA emulation that there is a parallel port available.
Looks like the answer should be in the CD that came with the conversion cable. USB is USB to Windows - it doesn't care which physical USB port is connected and will auto-find any devices.
One thing about Windows (any flavor) and USB is every thing gets mucked up when you plug new USB hardware in before running the installation CD - Always run the software first with USB stuff. If you think this is an issue - goto your Control Panel > System then Click Hardware Tab and then Device Manager button to view the ports that Windows knows about. IF there is a problem with one - it will show as either an Exclamation point or a Red X.
good luck !