If you bought pro for US $18.88 from the official site http://www.limewire.com/english/content/download.shtml then you should have received an email with a link to your personal pro downld page. You should bookmark that page. If that's not how you downlded pro, then you didn't get pro.

Which Java version are you running? It makes a difference! I'd recommend updating your Java to 1.5 & forcing LW to use it. See http://docs.info.apple.com/article.html?artnum=301073 in regards to making Java 1.5 your main java.

I'd also recommend deleting your LW preferences folder whilst LW is closed; found here /Users/your_username/Library/Preferences/LimeWire