GeCube X1950pro (AGP) problem?

Hey, I've just received the above named card but I'm having problems installing it. Window's start up recognises the new device. However, during the installation from the ATI disk I get an error message. The heading is "Severe" and it says something like "try installing standard VGA drivers first."

Now you're going to think I'm a total idiot because the recommended PSU for this card is 450W when my current PSU is 400W. Is this sufficient to cause this problem?

As a side note, I plugged my 9800pro back in and tried to use the new ATI driver disk but got the exact same error message!

Asus A8V deluxe mb
AMD 3500+
3Gb Crucial RAM