To select paper size, go to File->Page Setup… to change the paper size in each application. Then to change the various print settings, use the third dropdown menu from the Print dialog to adjust various settings. (At least, that's how it is for Mac OS X 10.4.)
I assumed you set up the printer following the directions, but they weren't written for Mac OS X 10.4. I tried to set up previously and didn't actually use the Epson drivers as I didn't do the printer selection correctly.
To set up properly, you have to make sure not to use the printer that shows up in the Printer Browser pane (as shown below) of Printer Setup Utility.
but click the button "More Printers…" Then, choose the Brand and connection setting (EPSON USB or EPSON FireWire, depending on which connection you're using). Then select the printer that shows up there.
Either select "All" to have all the Printer options listed, or sequentially add each Printer Page Setup. It's a pain that you have to go through all of this in order to make borderless prints, but that's how they've got it set up. I'm assuming you have Tiger installed on you Mac mini.