Not sure whether you are asking about the basics of using 2 monitors, or the specifics with Poser. My main screen is big enough for Poser, so when I'm Posering I use my second screen for email, web, file system browser, etc. Anyway, here are some basics...

There are different modes for using two monitors:-

Mirror mode, where both show the same content
Extended desktop mode (umm... self explanantory)

I don't know what the default would be if you attach another monitor to your card - mine started as Mirror. If it comes up as Mirror, then you just go into your graphics adapter properties and change it to Extended Desktop there. You should also be able to choose the relative position of your second monitor to suit its physical location.

Graphics adapter properties (on a PC) can be reached by using the graphics adapter System Tray icon (if there is one), or going into Control Panel Display properties and choosing Settings -> Advanced.

This is all assuming that your spare CRT monitor has a DVI input, of course. If not, you can buy a DVI to VGA converter - I have one on my iMac.

"If I were a shadow, I know I wouldn't like to be half of what I should be."
Mr Otsuka, the old black tomcat in Kafka on the Shore (Haruki Murakami)