VS 2010 Checkbox count and limit check and uncheck

dear brothers,

i am new to form, and learning some vb coding begining using vs2010

my question

i have 4 checkbox in a form

checkbox1,checkbox2,checkbox3,checkbox4

when i click the check box wants to select the checkbox aswell

and i have to limit the checkboxes only two want to select current

if i select checkbox3 it is select and any one of previous checkbox automatically uncheck for me

means two only limits the checkboxes

anyone help me to this code

thankyou