I'm not 100% positive, but since CS6 is on the verge of being released, the CS4 trial probably is not available through any official website.
Only the latest versions of the software are available as trials on the Adobe site.
As the otehrs said, there are no trials for CS4 products. If the Pro Design Tools workaround no longer gives access, then they are no longer there. God bless a good backup! Anyway, it's a moot point - why would you wanan run a trial of a product you can no longer buy? I'm even reasonably sure that CS4 required at least OSX 10.5.3, so it wouldn't run on your system to begin with...
BE FORWARNED: Think you're safe if you have a TIme Machine backup? Nope! If you restore your computer from an Apple Time Machine backup to a new hard disk, your legit, registered CS applications may not work. If you don't have the original DVDs, or if the original disks are damaged, you're stuck.
I had to replace my hard drive when it developed bad secors. Adobe Support's only answer: Buy the current version for $900.
Thanks, Adobe. If I could download a demo version of my older product, then there would be no problem. I could install and register it. Instead of satisfying a long time loyal customer, they've turned me into someone who will never buy another Adobe product.