I'm a newbie in programming so I'm kinda confused on how to do this:

msg me asap:[email protected](msn messenger) I am online as we speak.

it says:

Create a program with one textbox called txtnum and a listbox called lstresult. the textbox will be used to capture a positive integer greater than zero and after a button called btncacfactorial is clicked, the list box will be used to display that number's factorial. For example, if the user entered 3 in the textbox and then clicked the button, 6 (which is 3*2*1)shoudl be displayed in the lsitbox. Be sure to clear the listbox before you output the factorial for each number entered. ALso, bullet proof your program to allow only positive integers greater than zero; if the user does not enter a valid entry, give the user an appropriate message box.

I really need help on this. I have made the layouts with the textbox and listbos and the command button, but i desperately am lost on the coding, please help me.