I'm stuck on a 500mhz celeron myself. There's no reason you shouldn't be able to get an excellent system for under $500 from newegg if you're not a gamer. I tip my hat to you.
If you're not a gamer, don't even worry about the video card. I have a friend that's kickin' it on an old nVidia TNT2 card. The thing works great for him. Just get something cheap that is at least 16 or 32mb. Are you into any multimedia?