Thanks to you both. I was looking for a performance gain by going to 64 bit and if it's of marginal benefit and there's a few issues 32 bit seems like a no brainer.
I'll try not to ask too many stupid questions along the way. I have plenty of IT experience but ALL in the Windows space, I've never installed any distro even for a look before. So I've decided to use LinuxMCE and now I'm selecting hardware. Although I'm a little miffed at no Blu Ray support, but I do understand the reasoning behind the current position. It's no big deal though, hopefully decent content will be available for streaming from the web instead of buying a disc of any kind soon. Like an evolution of netflix. I'm planning on a lot of RAID protected storage.
Thanks again for your help