Hang on Boot

I expereinced the following with the released version of Vista Ultimate
available on the MSDN site.

1) On a Dell Inspiron 9100 (2 Gb RAM, 30 Gb available disk space). UPGRADE
installation proceeds flawslessly but hangs after setup is complete and the
first boot is happening. All the different F8 options were tried to no avail.
The hang appears to happen on the load of CRC232.SYS - but it could be
happening by another driver just before as well. On the same laptop, NEW
install worked successfully.

2) On a Dell Inspiron 9300 (2 Gb RAM, 30 Gb available disk space). UPGRADE
installation proceeds flawslessly but hangs after setup is complete in the
same manner as the 9100. I did not do a NEW install on this laptop, it may
work.

Note: On both laptops, any software (including anti-virus and firewall
software) that was flagged as causing problems for Vista was uninstalled.

I did get an upgrade install to work on an older Dell Latitude C800, so the
upgrade process did work on one machine.

Any thoughts on what could be causing this hang? Retail users are bound to
come across a lot of issues with upgrade installs if these issues are not
worked out.