Arin,
The Hover buttons use Java which requires that the visitor's computer have a
Java Virtual Machine (JVM) installed. Due to legal issues with Sun,
Microsoft quit distributing a JVM with Windows XP. Although users can
download a JVM from Sun (
www.java.com) you, as the web designer, can't
guaranteed that your site's visitors will have it installed.
Because of this, the normal recommendation is to not use the Java-based
Hover Buttons and instead use JavaScript (no relation to Java) or Cascading
Style Sheets (CSS).
If you wish to maintain the rollover type of effect that the Hover Buttons
give you, take a look at some of the JavaScript rollover solutions here:
http://www.dynamicdrive.com/dynamicindex15/index.html
You may also find useful effects here:
http://www.dynamicdrive.com/dynamicindex1/index.html
Good luck!