Browser compatibility issue document.getElementById vs. docu

[admin]

I've got quite an interesting problem, which I haven't come across before. I made an interactive form, so that if you select a category from the select list, the form below changes. In MSIE using document.all, this works fine, in netscape using document.getElementById this doesn't. It'll change once and never again. I'll provide you with a selection of the code I created, there is much more.
this is a major problem if i can't get this to work on both NS and IE, so i'm willing to take any suggestions.

Thanks,

Andy