Modules HELP URGENT!!!!!

i have written a program that when you select the file type from the combo box, the file1 box only displays file names of that type, how do i put this code into a module so that the module can read a letter from the combo box and depending on the letter the module will make the file1box display only that file type (depending on there choice, ie a = *.jpg b = *.gif etc...)
the code for the form is:

private sub filetype()change

if listindex = 0 then
file1.filename = (*.jpg)
elseif listindex = 1 then
file1.filename = (*.bmp)
end if

i want it so instead of saying file1 ETC after THEN, it assigns a letter or number to a veriable which is some how sent to a module that from the veriable it can assign file types to file names and go back into the form to do this!!!!
HOW THE ***** DO YOU GET A MODULE TO UNDERSTAND DATA INPUT FROM A FORM AND DOING SOMETHING WITH THAT DATA TO THEN GO BACK INTO THE FORM AND CHANGE THE FILE1BOX FILE TYPES AS YOU CAN SEE THIS HAS BEEN DRIVING ME MAD

I don't understand what you are asking, and there is no need to shout either.

wow.. I can't figure it out either, Doug - idd, can you be any clearer?