Also, after you register you are given access to be able to download a non-C/NET, non-downloads.com version of Bryce 5.
The advantage of this is that it doesn't need the machine ID-based activation. I believe this is probably a wise thing to do in case you want to install it on a replacement machine in the future, and the activation website is no longer supported.
To install the non-C/NET version you still need a serial number which is the portion of the activation code you're given on the web before the first ':' (colon character). It is *not* the whole activation code you use for the Downloads.com version. That may not make much sense right now, but it probably will once you see the activation code you get from the web.
It's a pretty big download - I don't know if it includes any of the content Deozaan mentioned or not.