Installing 32bit and 64bit OS on the same computer?

[Earth]

I want to know how to install 32bit and 64bit on the same computer? Can I partition off one hard drive and install seperately or will I have to install on two seperate drives and disconect the I don't want to use at that time when booting up?
Edit: OS is vista BTW

[newtech]

With either XP or Vista on two separate drives you don't have to unplug either if you are dual booting both edititions. To see each installed separately you then unplug one to see Windows installed onto the other along with a separate boot information record there.

[Earth]

Thanks for the reply.

I was intending to go with Vista Ultimate OS as I believe it has two disks of 32 and 64bit in the one package.

I don't know how to enable dual booting entries, but will try and do a bit of research. Will dual booting make the system slower?

[adept]

partition the drive into 2 parts...
and install both the OSs on each drive...
make sure you have all the drivers...