Host OS is Ubuntu 8.04 x86 32-bit with Windows XP SP2 running on Virtualbox. I
have an AMD 64 single core processor with 4 GBs of RAM and 512 MBs video RAM. I
have the XP VM set up with 640 MBs of RAM and 64 MBs of video exclusively for XP
and it runs fast enough for normal tasks, but I am not a gamer. It would be
faster with a multicore processor because Virtualbox allows me to tweak it for
multicore.

I am wondering if it would run faster if I ran 64-bit Ubuntu than 32-bit. I had
heard that it would run faster in 32-bit as Virtualbox sees the 64-bit as a
multicore. I am not sure if this is bogus, wishful thinking or misinformation,
hence my question.

I run 32-bit just for ease of use due to lack of 64-bit applications. I run
64-bit dsitros on other partitions and can't see that it makes any difference.