Before Ubuntu 6.10, I had no problems to access USB flash drives from Windows running under VMware (guest system) with Ubuntu as a host system.
And then Ubuntu 6.10 came and the problems came, too. Sometimes, when I plugged the drive, Windows detected it and I could access the data on it (rarely) and sometimes Windows didn't detect it at all or did detect it but there was no access to the data (usually). And I could see no pattern in this behaviour.
After a few months I finally found this article 3862823 in the VMTN Knowledge Base - USB Devices Are Not Available on Some Linux hosts, the VM > Removable Devices > USB Devices Menu Is Empty.
Adding the following line:
usbfs /proc/bus/usb usbfs auto 0 0
to the /etc/fstab file solved the problem.