I have a problem with my display setting, it says the highest is 32bit
but my windows vista is 64bit ultimate ,my graphic card is NVIDIA GeForce 8500 GT, and my CPU is Intel QuadCore.

what is problem? why i cant increase it to 64bit????

Your getting 2 different things mixed up

32 bit display settings referes to the amount of different colours sent to your monitor Color Depth.
TFT's cant display anymore that 32 bit anyway (or 24bit true colour) so thers no need for anything higher than that/

A 64 bit processor, running a 64 bit operating system ie. Vista x64 has to do with the commands sent around the computer. A 64 bit processor can use more instruction sets & memory addresses(busses).

64 bit could also refer to the size of the busses(information connectors like having more lanes on a road, mean you can sent more stuff at ones)

Monitors can only display 16,777,216 Colours which is 2^24.

16,777,216 comes from 2^24, the number of combinations of 8 bits each worth of red, blue and green.

The extra 8 bit (in 32-bit colour) is the alpha channel is used more for image blending and transparency than for colour control.

2^# of bits = total colors
Typical bit depths are 8, 15, 16, 24 and 32 bits/pixel translating to:
2^8=256 colors
2^16=65,536 colors
2^24=16.7 million colors
2^32= also 16.7 million colors!
32 bit color is (in almost every instance) really 24 bit color with an 8 bit "alpha channel."