Rearranging strings vb 2008 express edition

Hi,
I have an assignment for my college vb class that Im not sure how to tackle. I need the user of my program to be able to enter in a five letter word, and I need to output every possible combination of 3 of the letters into a label.

I know how to do the output, Im just not very good at string manipulation. (Im not familiar with many of the functions and methods neccessary, besides easy ones like indexof, trim etc.)
I was thinking of splitting all of the letters into a seperate variable using substring, but im not sure if that overcomplicates it. Please help.

Thanks.