Oki C 5400n - Manual (Page 248)

Windows: Postscript Emulation Driver • 246
6. On the Layout tab., click Advanced .
7. In the Paper Size drop-down list, select Postscript Custom Page
Size .
8. Define your custom size in the dialog box which appears, then
click
OK twice.
9. Click the Paper/Quality tab and select the feed tray you are using
for the custom size paper from the Paper Source drop-down list.
10. Windows XP only: click OK to return to the Print dialog box.
11. Click Print .