Re: 6600 GT AGP vs 6800...
Depends what setting you wanna play at, and your budget. The Gigabyte 6600GT AGP sells for $199. The cheapest 6800LE sells for $249, and that's for a no-name brand. If you're like me with an LCD that cannot go beyond 1024x768 and your AA/AF use is moderate, then a 6600GT is a much wiser investment. For overall speed the 6600GT and 6800LE are on par, but the 6800LE has a 256bit memory bus so it's added memory bandwidth helps with AA/AF. And obviously if you get a 6800LE (8 pipes) or 6800 standard (12 pipes) you have the slight chance of modding it to 6800GT (16 pipes).
So it's up to your budget and your gaming use. Both are excellent and will serve you well, but I would advise you not to purchase a no-name brand.
Athlon64 3200 Clawhammer / Asus K8N-E Deluxe / 1GB Crucial DDR400 / Geforce 6600GT 128MB AGP / Windows XP Pro