two <IF>???

[Chewy75]

I will try to explain exactly what I want to do, perhaps I am goning a totaly wrong way...

If you select thread-view or hybrid-view in a thread, then you will see a tree-structure in top of the postings in that thread. This tree structure is normaly 150 Pixels high. What I want to do is to allow users to change this height by their own.
I found the height in template: "showthread_list" and I thought best way to solve my problem is adding a field for the users selection and adding some little code to this template, but I am not a real coder so I looked arround for the syntax and so on and thougt the code of my frist posting would be near to that what I need...