Start out by uninstalling McAfee it is known to cause problems with LimeWire. And what version of Java have you been downloading. You need Java 6 For Vista. You can get it at the link below. Use
Java Runtime Environment (JRE) 6u1 and choose the
Windows Offline Installation, Multi-language If you do not have Java 6 uninstall all versions of java on your computer. Then install Java 6.
http://java.sun.com/javase/downloads/index.jsp