Sadly, our installer guys don't seem to comprehend testing all scenarios or even code inspection.
This installer bug has been fixed in the Fusion 3.0 releases though, and I personally tested it myself, 32 and 64 bit VMs both.
However, did you try the workaround for the installer nonsense? That is, uninstall the VMware Tools using the control panel Add or Remove Programs, reboot VM, do your upgrade to Fusion 2.0.5 and
then install the VMware tools, reboot the VM.
This should then get your network drive mappings working. If you did the above and the drive letter access still fails for some reason, then you are hitting a different bug.
Thanks.
Steve