As a beginning, open the report in Design View, then choose Print from the File menu. Set the Name to the printer driver for the dot-matrix printer. Then click the Properties button. The properties dialog you see depends on the specific printer driver installed, but somewhere in it it should have a Paper Size setting. The last choice in this list is Custom; when you click it, it will present a custom paper size dialog where you can enter the length and width of the page.
You will probably also have a property (mine is called Paper Source) where you can choose between Page Break and No Page Break. Try choosing No Page Break first. I think that if you choose Page Break, you'll only print one check per page.
After you've made the properties changes, you'll return to the Print dialog. If you're not ready to print yet, DO NOT click Cancel, because this will undo the property changes you just made. Instead, click the Print To File check box, then click OK, and when the dialog comes up asking for the file name, click Cancel. You may get an error message, but your property changes will have been saved.
If you're printing from a Form, make sure that the form's height (the sum of the heights of its Header, Detail, and Footer sections) is equal to the height of a single check. If you're printing a Report, the same concept applies, though you probably won't have any page or group headers or footers, so only the report Detail height is counted. Rick Sprague