Your printed colors can never exactly match your on-screen colors. However, you can use a color management system to get as close as possible. Try using the ICM (Windows) or ColorSync setting (Mac OS X 10.3 and 10.4 or Mac OS X 10.5 [in the Color Matching pop-up menu]).
After you print, the colors on your printout will take some time to set as the ink dries. During this time, the colors may look different than you expect. To reduce the drying time, avoid stacking your prints on top of each other.
For best results, use genuine Epson ink and paper.