Vista compatibility is a top priority for Arduino 0010. In the meantime, it should be possible to get work with Arduino 0009, but will take some doing. You need to download the latest version of WinAVR. Then, rename the tools/ directory in the Arduino application directory. Copy the WinAVR directory into the Arduino application directory and rename it "tools". You might also have to move some of the files in the WinAVR directory so their locations correspond to the ones in the original tools directory. Then, you'll need to copy the original tools/avr/bin/avrdude.exe and tools/avr/bin/avrdude.conf into the new WinAVR tools directory (in the same sub-directories). People have had success with this with Vista 32 bit. With Vista 64-bit, I'm not so sure.