According to the documentation for the Epson Artisan 810 all-in-one printer, the only way to print onto CD/DVD media is via the Epson Print CD program. But what about printing from any other program? (The Discus label program comes to mind.)
There's a bug in the Epson driver as of June 2010 that prevents selection of CD/DVD media from either the Page Setup or Print dialogs. (The media is shown but it's permanently grayed-out.)
The workaround, courtesy of the folks at Magic Mouse (developers of Discus), is to first choose a paper size of A4. After doing so, the CD/DVD media choice becomes available in the Print Settings section of the Print dialog.
When Epson fixes the driver or at least enters a FAQ explaining the workaround, I'll delete this page.