It's possible you don't have the same jvm in use in your browser as you
use in the appletviewer.
What jvm is in use in youyr browser, what does the java console say, and
what does the status bar on the browser say.

i suppose that u prefer java swing interface classes, or u maybe use some of new
java classes that releases after 1.2 release of java. And also your ie has no
active java
pluggins on.

there are two solution.
1- dont use the classes which are unspupported by microsoft java vm
2. use java pluggin!