You didn't say which Operating System (OS) you have so I'll guess it's Bill'$ windows. I can't see anything about yur modem being a blocker though I haven't had a thorough search yet.

Update your Java: Java 1.4.x OR else Java 1.5 (take the JRE) & see if that improves things.

You could also delete your LW prefs folder called: .limewire & found here: C:/Documents And Settings/your_username/.limewire