Did you install Ubuntu inside Windows using Wubi? Or did you install Ubuntu to it's own partition on the hard drive?
If you installed using Wubi, then just delete it from Windows control panel. If you installed Ubuntu to it's own partition, simply reinstall the new Ubuntu to the same partition.
I don't think that using 64bit instead of 32bit will solve any problems you may be having. You can use 32bit Ubuntu on 64bit computers. I do.
If you used Wubi, I would recommend doing a real Ubuntu install to a dedicated partition on the hard drive. Ubuntu will run better that way anyway.
See this site for getting started with Ubuntu:
You don't have to get rid of WindowsXP to install Ubuntu. You can easily dual boot both Ubuntu and XP on the same computer. I do. See this site for dual booting Windows and Ubuntu:
And you can get the free Ubuntu manual here:
Write back if you need more help.
And welcome to the LQ forums!