So far I've purchased two different brands of USB-to-Serial adapters which work great in the Mac world (Intel iMac V4.6), but not in an XP VM. One problem is that they are very slow. They will work with small data bursts, but cannot sustain data flow at even 9600 baud. At this speed, they drop more characters than they pass. My guess it is either a flow control (handshake) problem, or the transfer buffers are just to small. No problem in the Mac world since both have been tested to 115.2 Kb. My second problem is being able to consistantly bind the USB-to-Serial adapters to the VM. Seemingly at random the VM will say it can't bind them because they are being used by another process. I assume this means that OSX has assigned them to some process, but I can't find out what that is. I've looked at the processes running and don't see anything that would use the these adapters. I'm relatively new to the Mac world and might be missing something obvious. Sure could use some help running this problem down. Finally, a question about drivers. Should both the OSX and XP drivers be installed, or just one of them. I'm not sure at what level hardware resouces are bound. I've written over a dozen Emails to Parallels support, gotten back a dozen robot responses saying they'd get back to me in 3 days, but haven't heard from them in 60 days. I was going to try to use virtual serial ports using Unix or TCP sockets, but I'm afraid this is beyond my skill set. I must take nightly sleep studies using a pulse-oximeter and use this information to adjust oxygen flow, medication, etc. Unfortunately the only software available for this instrument is for the Windows platform and the only hardware interface is a serial port. Sure could use some help... please!