Hello to all the members ot this forum 
First of all I want to apologize for my bad english.
I am new to access 2007, and totally noob , but i realy need some major help on one question , that i have no one to ask.
So , the deal is like that: I have two tables - tblStudents and tblPayments
In tblStudents lets say I have two columns - "IDNumber" (auto number) and "FirstName" (text field)
In tblPayments i have "ID"(which is the auto number of the payment and is not related to the problrem) , the next column is "IDNumber" (Long Integer) , after that i have "FirstName" (Text field) and finally one field for the money that they pay , but that is not the point.
I need to make a form of tblPayments in which when i fill the "IDNumber" manually (not from a combo box , because the numbers are like 1000) , then the second controller - "FirstName" automatically to return the name of the student. So i spend two days reading for DLookUp functions , but i am not getting any progress at all. I have tried many things and nothing worked, i get the same mistake -
"The expression you entered contains invalid syntax"
So i started from the beigining and tried only a A Function with No Criteria:
= DLookUp("[FirstName]", "tblStudents")
(which i wrote in the field Control Source of the controller "FirstName") and I get "The expression you entered contains invalid syntax"
so I have treied :
FirstName = DLookUp("[FirstName]", "tblStudents") , and
= DLookUp("FirstName", "tblStudents")
and so on and on .....
Not to mention that in the beginning i have tried the full function :
=DLookup("[FirstName]", "tblStudents", "[IDNumber] =" & Forms![Payments]!IDNumber)
FirstName=DLookup("[FirstName]", "tblStudents", "[IDNumber] =" & Forms![Payments]!IDNumber)
=DLookup("[FirstName]", "tblStudents", "IDNumber=" "IDNumber"
and so on and on.... everyting was wrong
Please help me just with the Function with No Criteria ,and i think i can handle it from there.

First of all I want to apologize for my bad english.
I am new to access 2007, and totally noob , but i realy need some major help on one question , that i have no one to ask.
So , the deal is like that: I have two tables - tblStudents and tblPayments
In tblStudents lets say I have two columns - "IDNumber" (auto number) and "FirstName" (text field)
In tblPayments i have "ID"(which is the auto number of the payment and is not related to the problrem) , the next column is "IDNumber" (Long Integer) , after that i have "FirstName" (Text field) and finally one field for the money that they pay , but that is not the point.
I need to make a form of tblPayments in which when i fill the "IDNumber" manually (not from a combo box , because the numbers are like 1000) , then the second controller - "FirstName" automatically to return the name of the student. So i spend two days reading for DLookUp functions , but i am not getting any progress at all. I have tried many things and nothing worked, i get the same mistake -
"The expression you entered contains invalid syntax"
So i started from the beigining and tried only a A Function with No Criteria:
= DLookUp("[FirstName]", "tblStudents")
(which i wrote in the field Control Source of the controller "FirstName") and I get "The expression you entered contains invalid syntax"
so I have treied :
FirstName = DLookUp("[FirstName]", "tblStudents") , and
= DLookUp("FirstName", "tblStudents")
and so on and on .....
Not to mention that in the beginning i have tried the full function :
=DLookup("[FirstName]", "tblStudents", "[IDNumber] =" & Forms![Payments]!IDNumber)
FirstName=DLookup("[FirstName]", "tblStudents", "[IDNumber] =" & Forms![Payments]!IDNumber)
=DLookup("[FirstName]", "tblStudents", "IDNumber=" "IDNumber"
and so on and on.... everyting was wrong

Please help me just with the Function with No Criteria ,and i think i can handle it from there.