create a form for asking a customer, i.e. with a combo box having rowsource of cust_id or what ever u want. then create a command button. In wizard select record operation and select the report u want to run in preview.
then open the code of the command button
it shows:
DoCmd.OpenReport "ur report name", acViewPreview
add the where condition for ur cust_id in this code as:
DoCmd.OpenReport "ur report name", acViewPreview, , "cust_id = "& forms![ur form name]![ur cust_id field name on the form]
if the cust_id is of text datatype than add single quotes i.e. " ' " before and after the forms![ur form name]![ur cust_id field name on the form].