Having entries present information

Hi all, what I'm attempting to do is basically have a box where I can put in a 3 digit code (ABC or 123) and when I put that in the box, it will pull
information from another sheet in the spreadsheet and present it on that screen.

How do I go about doing such a thing?

i.e. if I had a Sheet2 that read:

ABC: abcdefg
DEF: bcdefgh
HIJ: cdefghi

and I type "ABC" in Sheet1, it would present the info "abcdefg", and if I typed in "DEF" it would show bcdefgh. Obviously I'm simplifying this for argument's sake, but hopefully that's as descriptive as you need.

I'm using Excel 2003 if that makes a difference.