How do I connect my PC to both my monitor and TV: particularly with a splitter?

Like many people I have a desktop, including CPI and monitor, running on Windows XP.
I also have a television: specifically a Samsung flat screen.
My CPI seems to have only one RGA port, though I have a splitter as well.
When I connect both TV and monitor to the splitter, the monitor darkens a little and the TV says “PC” and “Mode Not Supported”.
How can I get video on both TV and monitor?
Thanks.