[ddouglass]

If you purchased 3.319 in January then you didn't need to purchase 3.321 as it would have been a free upgrade. Did you purchase 3.321 as an Upgrade or did you do a full purchase again? This will make a difference in the registration code you use.
When you start the 3.321 installation the second time (after the 3.320 removal) what is it telling you when it won't install? Is there an error message window that pops up or something in the installation program that tells you it won't/can't install? There are too many causes for it to fail to install to list without knowing what exactly is going on.
Phoning MTU will not help as they do not do telephone support (too few employees) and only use the Support Email for that. And they will be asking the same questions.