Video card and video playing issues, any help appreciated

[PJ_OSX]

I just installed OSX 10.4.8, upgraded to 10.4.9 and then to 10.4.10. I have a Intel P4 915G chipset, I am currently using the onboard video and realtek onboard audio.

Two questions now, when I had my ATI x600 PCI-E card in the apple would load on my screen and then when the os was supposed to load up I would lose video connection and just have a black screen, so I removed the card and started using the onboard and then video worked, I thought that the radeon x600 was supported though? So if anyone could help me get that card back up and working that would be great, next thing, I can't get dvd's to play, I tried Mplayer and FLV, and some videos come out choppy or just won't play, I got one vcd to work right out of all my media. What do I have to do to get my dvd movies and video files working right? I am very new to this, used Windows all my life but the appeal of the Mac OS drew me over, I don't know much about scripting and codes I have only done one edit to the boot to get my monitor resolution correct, but if that's what I have to do to try to get this stuff to work I'll try my best to understand the help I'm given, and if I can't get anything to help me I'll just go back to XP. I'd appreciate anyones help, thank you!