what model is it (5200,5600,5700,5800,5900,5950,Normal,Ultra,XT?)
i noticed the same thing in a way with going from a 64mb leadtek gf4 ti4200 to a 128mb gecube radeon 9600xt extreme. it worked pefect in esf for the first few days but then , even after getting latest drives , then reformatting , then getting newer drivers made no difference for esf (but ati has it's problems , i sold the card) now i am just using my bro's fx5200 , with 1.2 i run it at 1024x768 on opengl high quality , no probs (just have smoke turned off after beams since it can lag a little afterwards) running it on a athlon xp 2400+ ,512mb ddr33 memeory and asus a7n8x-e deluxe board
EDIT: If u update your drivers it could make a difference , with form what i have seen in benchmarks the later drivers can work a lot better most of the time