Dominic
I believe you can accomplish what you need to by using going to the menu Data>Validation. This function will allow you to specify the input criteria acceptable from the user. In your case, you'll want to choose (under the data validation dialog box, Allow:) "Whole Number". From there, you can specify a range, for example, a minimum of 1 and maximum of 5000. If the user tries to enter text, they will get an error message. You can even specify what you want the error message to say by clicking on the Error Alert tab and filling your message in. If the numeric options are very limited, you could also choose "List" from the "Allow" box, and put in the only valid choices, i.e. "1,2,3". When you use List, you can also make those choices available in a drop-down cell so the user doesn't have to type them. Hope this helps.
Thanks, An excel function that I did not know