Oh, if it were only that easy.
Basically, in order to figure out what kind of entries the installation program put in your registry, you'd have needed to have a Registry Logger of some type running (such as Norton CleanSweep) that would detect any and all changes to your registry and other files, so that you could remove those changes later.
Once installed, the install program is likely to have scattered changes throughout your registry and to other files in your \Windows and \Windows\System directories at least. There are many devious ways to hide "keys" that store the installation date, and graphics software developers are literally at the cutting edge of this type of work, because their programs are so expensive to design and will sell relatively few copies (compared to, say, Microsoft Word), so they MUST recoup every penny possible.
Anyway, your only hope now is to find a "crack" for the exact version of the software you installed. Assuming it works, and isn't a Trojan Horse program that wipes your harddrive or installs a virus, it hopefully will go and delete all of the magic "keys" left behind and restart your 30-day clock...
Either use a search engine, or go to the newsgroup "alt.cracks" and ask for one.
-Troy