Stumbled across this the other day and it really does work I have been using DivX products for about 10 years now since the Dr. was in the house.
MAKE SURE THAT YOU UNINSTALL THE DivX v7.0 PRIOR TO THE INSTALL OF v8.0 PLUS OTHERWISE YOU MIGHT BE CONFRONTED WITH THIS AND HAVE TO TOTALLY REMOVE v7.0 and v8.0 FROM YOUR REGISTRY BEFORE THE UPGRADE
If you do get this then I suggest using jv16 Power Tools v184.108.40.206
is FREE but it is limited to what you can do the full version now @ v220.127.116.110 @ time of posting you can get from HERE
if you can afford it then you should get REVO Uninstaller Pro check out my tip HERE
for help and advice plus a 20% discount. This application is a much easier and 99.99% guaranteed to work to remove registry key and leftover folders even from previous uninstalls.
Sometimes after the upgrade you will not see the serial numbers like above or you may just see the DivX Plus Convertor 8.0 serial on the control panel it will just say registered if you want this to show you need to create a reg file replace the "" with your 20 digit serial that you purchased and all will now SHOW on the control panel the latest version of the procodec is v6.9.2
Windows Registry Editor Version 5.00
The new DivX Pro v8.0 bundle that includes HD support can be purchased at a saving of $7.00 (£4.60) try it now at THIS
link and use it with AutoGordianKnot, VirtualDub and many more AVI convertors as the alternative to the free XviD from libavcodec.COUPON CODE : 30OFF
If you already own DivX Pro v7.0 you can upgrade HERE
and get upto 50% OFF the retail price of £12.99 that is a saving of £7
If you really want the SRS-WOW plug-in and the MPEG-2 plug-in you can but them as a part of this upgrade and save money on VAT, note it tells you that it will cost £6.49 for each one this is a mistype when you actually upgrade its much less.
NOTE support for DivX v7.0 Professional runs out at the end of April 2010 find out what this means HERE
if you are not sure whether or not to upgrade.