I have been using a Gold-X GXMU-1200 USB to RS232 Converter for almost a year now and it works great.

The Gold-X uses IRQ addressing instead of Windows system calls, so it works with older DOS based programs.

I had to switch to the Gold-X so I could use my laptop with software like the Comdial DX-80 and the Toshiba Stratagy voicemail use.

It works great and I haven't had any problems at all.