Like a few people on the forum, I would pre-buy Fusion if serial would work.
I'm using vmware fusion beta 4 now. I have the IOGEAR GUC232A usb to serial adapter. It shows up as /dev/cu.PL2303-000033FD under mac osx. serial works in osx. I have some ancient serial HW that only works in win95 that I'm trying to debug/hack. portmon is not working in win95 on my real HW for some reason, but it is in vmware?
Here is what I did. Editing the .vmx file
1. I edited my /Users/maniac8/Documents/Virtual Machines/Windows 95.vmwarevm/Windows 95.vmx and changed the serial port to the following.
serial0.present = "TRUE"
serial0.fileType = "pipe"
serial0.fileName = "/Users/maniac8/tty1a"
serial0.tryNoRxLoss = "TRUE"
2. I installed socat via macports. http://www.macports.org/
sudo port install socat
3. I used socat to "link" my pipe to the device. (I'm not sure if ispeed and ospeed options help)
sudo socat -d -d /Users/maniac8/tty1a /dev/cu.PL2303-000033FD, ospeed=9600, ispeed=9600
Now when I bring up hyperterm in win95, I get the serial data from the device, but the device driver still isn't noticing the data? Now I think maybe there are timing issues in the driver.
BTW, During debugging of this, I used
sudo socat -d -d /Users/maniac8/tty1a PTY:
then look for which ttyp socat assigns. mine was always 3 and I set hyperterminal baud rate to 9600, so I open another terminal and type
screen /dev/ttyp3 9600
This lets osx and my windows communicate through serial, but my device still doesn't work 
I'm not really familiar with vmware or socat so maybe there are options that will eventually make this work for me.
In the meanwhile, I hope this helps someone 
Hasta,
Maniac8