hi,
wht brand ur card is of (e.g Asus, MSI etc) and if it isn't of any brand then it may be a remarked card. I use to have same graphic card in the past but it isn't of any brand. Offcourse it shows memory when system is booting to be 64mb but in windows under DX9 it shows its real memory which was 32 mb. It is actually of 32 mb but they somehow make it to show its memory when system boots to be 64mb.
Changing the drivers won't solve this problem if its remarked. It may for instance show the memory to be 64 mb under windows also but after sometime it will start to show its real memory again which is 32 mb. That's wht i learnt from my experience. :grinthumb so chk if thts the case with u also.