Hi Debra,
My following instructions are for Windows (since that's what I have) but instructions for other platforms should be similar...
In the printer driver settings, click on the Paper tab. Then on the Paper Size menu, choose User Defined. A new box will come up. Set the paper width to 1700 and set the paper height to 2500. (These are in 1/100ths of an inch, so the numbers really correspond to 17 inches and 25 inches.) Enter a name of your choice (e.g., "17x25") into the Paper Size Name and click the Save button. Click OK.
Now (and in the future) whenever you want to print on 17x25, just choose 17x25 from this list.
(Also make sure to set the Portrait / Landscape orientation appropriately.)
Eric