Layout problem

Can someone take a look at

http://www.thad.demon.co.uk/tsr/index.htm

This should auto link to index640.htm or index800.htm
(It does in all versions of IE and Netscape that I have)

The 800 is launched if the user screen is 800*600 or better
otherwise 640 is launched

I am concerned about the 800*600 setting

In Netscape (any version) it behaves as I expect -
    i.e. man frame with vertical scroll but no horizontal scroll
In all version of IE BEFORE 6 it also worked as expected
 but IE6 has a horizontal scroll

Any one tell me why and how to fix it?

Allan Smith