Need help with access form

I have a Data entry Form to enter the payment info. I have Invoice ID and Invoice amount etc... in Invoice Table. I want the Invoice amount to appear automatically in the Payment form based on the Invoice Number I enter. I have Invoice number in both tables, Invoice Table(Primary Key) and Payment Table (Foreign Key).I have attached a sample DB, and my DB is similar ti this sample DB, just bigger with more fields.
Thank you for your help.

Please read this: http://www.excelguru.ca/content.php?184

cross with response at: http://www.accessforums.net/forms/need-help-access-form-31595.html

Here's a modification of your form.

Avoid using spaces and other special characters in object and control names. Also consider implementing a naming protocol along the lines of; TBL_TableName, FRM_FormName, QRY_QueryName etc.

Lucky I'd done all that work before I saw Alan's post.