Download the trial from http://prodesigntools.com/all-adobe-cs5-direct-download-links.html
Ensure that you follow the Very Important Instructions on that page first otherwise the links will not work.
Activate the trial with your serial number.
John, for CS5 downloads, I tried to select acrobat pro9 and Web Premium got:
You don't have permission to access "http://trials2.adobe.com/Applications/Acrobat/APRO/9/trials/AcroPro90_ efg.exe?" on this server.
Same with web premium
You don't have permission to access "http://trials2.adobe.com/AdobeProducts/WEBB/CS5/win32/WebPremium_CS5_L S1.exe?" on this server.
What did I do wrong? Using fireworks, I undid "Block reported sites" etc - help!