Update your Java. Use the JRE offline installer here & remove any old Java version before installing the new one.
http://java.sun.com/javase/downloads/index_jdk5.jsp

You could also try Java 6 if the other update doesn't help. Again, remove your old Java version before installing the new.
http://java.sun.com/javase/downloads/index.jsp

Double check your XP firewall setup.
Firewall setup