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there's options in ipb adminCP under XOOPS settings/common settings where u can select which method to use.
regarding your skin, what skin is it? also if ur old forum had any hacks installed that included modifying the skin files they will most probably not work and cause a blank page.. if thats the case, remove the hacks and then redo them afterwards.. some hacks may need converting to use..
your best bet of support for x-ipb is on bbpixel.com instead of xoops.org..