Suggestion 1 
Write a program to ask a user for their name and output their name in reverse order.
Such as:
Input: James
Output: semaJ
Suggestion 2
If you fancy a harder challenge try Airwaves suggestion:
Create a program to create users and encrypt their password and store the encrypted password in a file with their user-name.
Then allow login with user-name and password validating the password.
To make it harder still, write it so that even if someone can read the SmallBasic code they still cannot decrypt the password (although they could bypass the validation by altering the code).
That is: given the code and encrypted password they cannot back calculate the correct password.