Swannsmart external modem is not always detected in XP mode vm

Hi crew, when I start xp mode my modem is only occasionally detected correctly.
Most of the time, when xp mode queries the serial port during vm boot-up, the modem does not respond correctly. xp mode appears to retry the detection a few times in quick succession.
The modem never fails on [any] real hardware, only on the virtual machine.

IfI click 'scan for hardware changes' in xp modes device manager a few times, it eventually is detected properly and appears in device manager.
On some restarts of the vm, the modem is detected correctly first time, but not often.

It's a 56k voice/fax/data modem made by Swann, with the Ambient [now Intel] chipset.
In fact, if I let XP mode search the net for a driver, it loads a 'Intel v92 external modem' driver.

But of course, the driver is not the problem, it's the initial querying of the serial port to see if anything is connected to it that's the problem.

Here's a short youtube vid of the problem with explanatory text in the vid.

Host OS is a up-to-date win 7 ultimate x64 sp1
MB is a Foxconn P965 LGA 775 with a Q6700 quad processor.

Any suggestions/tricks most welcome

an update:
it's definitely an xp mode issue. vmware always detects the modem correctly.

This seems an unresolvable issue with xp mode, so I'm sticking with vmware.
It's actually a bit better than xp mode in that I can drag n drop directly from the host file system onto a virtual app running in unity mode on the host desktop....brilliant!!