Thank you for your post.
Yes, you can create a many-to-one relationship. If you type in the part number, the portal can display all records that match that part number. You can then decide which part number you want to use. To create a portal, go into Layout Mode, and on the left side of the screen will display tools. The icon just below the oval tool is the portal tool. Click on this icon, and use it to create a box on the layout that will display this information. After drawing the box, a dialog box will prompt you for which table you want to display (part numbers), and then another dialog box will ask for which fields you want displayed (description, price, etc.). If you return to Browse mode, enter a part number, the portal will display all records from part number table that match that part number in the purchase order.
A repeating field is one field with many values. What you may want to do is create another table with the same fields you want to export. Then, import from the original table, and you will be prompted for what you want to do with repeating values. You want to split them into separate records. This allows you to then export all of your records to excel.
Let me know if you need clarification for any of the above steps.