I went through Google and within 15 seconds I found this.
It talks about solutions on how to fix a Java 1500 error. Even if the solution is for Vista, 2000, XP, and 2003, chances are it will work on Windows 7.
Hope that helped.
Whenever i try to install JAVA on my windows 7 beta, it tells me that im having another installation and i cant install it. it also sais Error 1500