If you are new to Linux, you should not install Fedora Core 6 test 3, or any other test version of Linux. This is not a fully tested version of Linux. It is just what it says, a test release, meant for those with experience with Linux to test for Fedora and give feedback.
I am having a little trouble understanding what you did, please explain more fully.
It sounds like you did a text install and not a graphical installation? Did the installation complete fully?
According to ATI, it should be supported. See the ATI article
here.
Could you provide a little more information?
Is this a non-athlon 64 processor in your system?
What is the make and model of your system?
Did you use the correct iso of Fedora for the installation? In other words, what ISO images did you burn to do the installation? The non-athlon 64 images, or the x_64 version for an Athlon 64 system?
Did you attempt to configure the video card and monitor during the installation at the hardware summary screen?
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"I love it when a plan comes together." - Hannibal Smith