TI-89 Calculator Programming Help

Recently, I've begun to mess with the programming features on the two calculators at my disposal.

My TI-83+, has the simple programming that is easy to figure out. I wrote a program to perform various calculations based on a missing variable in a radioactive decay equation (y=n(e^kt)). e being natural base.

It looks something like this on the first few lines:

RDECAY
: Menu("Missing:","K",a,"N",b,"Y",c,"T",d)
: Lbl a
: Prompt N, Y, T
: ln((Y/N))/T->K
: Disp K
: Stop
: Lbl b
: Prompt K, Y, T
: (Y/(e^KT))->N
: Disp N
: Stop

Etc, Etc, Etc, you get the point.

Now in the last two days I have been fiddling with my brother's TI-89 Titanium, and of course it couldn't be somewhat similar and simple. The language of the programming is slightly different from the 83+ version(quite different actually).

Basically what I am asking is if anyone knows of an option on the 89 system that is just like "menu()". I know of "popup", but it isn't working with the "Lbl" format from the 83+ version. I have scoured the internet for answers and have found none.

I do realize that the type of programming I am asking for is very simple in terms of programs that can calculate circles and other complicated crap, but I really only need it for variable management.

Jam it back in, in the dark.