Am a little confused
You want to install XP alongside Vista, yes? But what is the issue? You second post seem to say you have succeeded already.
If you want to have 2 OSes, you need to create an extra partition.
Also, keep in mind that the usual process of installing multiple OSes is to install the oldest one first, followed by the newer one. If you reverse the process, the older OS may not recognize the boot manager of the newer one and may overwrite it. In this case, you'll need to fix the boot manager.
A word of warning. Do NOT install Windows XP 64 Bit with Vista 32 Bit
