How to autofill fields using a form, using access2010

I am a Rotarian and we have a program called Student Stay In School Program with 49 active students at the present time. I been given the task to set up a data base to record student costs re: Tuition Fees, Textbooks, etc. etc. I have the Tables, Queries, Forms and Reports set up and working fine. Now I would like to be able to auto fill fields when entering expenses with the expense form ie: enter the Student ID # and it would auto populate the Student First Name and Student Last Name. My Student Table, StudentT, contains all the student information. My Expense Table, ExpenseT, all the expense information plus a StudentID, not a Primary field.

Thank you.
Art Borzel.
S.I.S. Committee Chairperson.
Rotary Club of Calgary South.