Jude Alvia

Currently have a pc with oem vista ultimate 32bit. I have a retail version of vista ultimate and trying to decide what version of vista (64bit or 32bit) to install on a totally new (just built) computer. Very pleased with performance of my vista 32bit computer but the new one is going to be my toy. Any suggestions or opinions are appreciated. Is there any reason I wouldn't be able to install vista 32bit now and then later install 64bit later on down the road (like when it has more compatibility with programs)?

Thanks in advance for input.