I upgraded one of my customers and I used the CRM 4.0 90 day trial key and
it did seem to convert my customer's v3.0 to a v4.0 key as they still have
the same # of CALs registered, etc in deployment manager in CRM 4.0.
However, to be on the safe side, you should have your CRM 4.0 reg key handy
and I believe that is what you are looking for. You should be able to find
your unique CRM 4.0 key embedded in a text file on the media you download
from your eOpen site.
If this doesn't appear on your eOpen site and/or you want real media, you
will have to call worldwide fulfillment at 1-800-336-0098, option #4 and then
option #1 and provide your eOpen authorization and license number.
Because you had software assurance when you bought CRM 3.0 you can then
order the CRM 4.0 media that will have the license key either on the sleeve
and/or embedded in a text file.
I hope this info helps, and this may not apply to your unique situation if
this is a MSDN license, etc.