I'm planning installing Windows XP on a Mac running virtual box and was wondering if it makes a difference between 32 bit and 64 bit edition? If both can run fine I guess I'd go with 64 bit since it's faster.
Whether or not you can run 64bit guests depends on whether you're CPU has the VT-x extension flag on the CPU. If it doesn't, you will be unable to run 64bit guests, regardless of whether the host (e.g. OS X) is 64bit or not. I would recommend you stick to 32 bit, you really don't need the extra performance, nor will you see it when running an OS virtually as a guest within a host OS.