The HD5770 uses the same drivers as the HD5450. There is no need to change them. You may want to update to the latest version on the AMD site though. Always ignore the driver cd; it is undoubtedly outdated.
It is a good card. It's pretty good at 1920x1080 and great below that.
Nvidia's cheapest worthwhile competitor is the recently released GTX 460 for $200. It's about 20% faster and a pretty good deal. It's worth considering if you have the money and a monitor with a native resolution of 1920x1080 or above.