ati AIW x800xt problem

[Witzode]

i recently bought an all in wonder x800xt 256mb video card with an AMD athlon 64 3700+ and asus KV8 x-se motherboard and 1 GB of OCZ enhanced latency ram... i only have AIM running in the background and games lag tremendously. i have to run games at 800x600 for them to run smoothly. the minute i put the resolution up to 1280x1024 or even 1024x768 everything gets all laggy. WHY IS THIS? ive read that people run games at 1200x1600 with no problems using thisvideo card. im not even using AA or AF. someone please heelpp me. any advice would be appreciated.