I am still working on choosing how to run my main HTPC. I ran XBMC on my wxp desktop, but when I woke it up from standby, it still required me to log in to the windows user (the PC only has one user, and it doesn't have a password). I'm reading about OpenElec and it looks pretty good. It can use add-ons, which is awesome. http://lifehacker.com/5851924/openelec-is-a-hassle+free-xbmc-distribution-for-home-theater-pcs
But then again, I would like to use my games. If I can find a way to run it on WXP without ever seeing the log in screen, it would be awesome! That way, I could easily close XBMC and work on the back end with no coding knowledge. In that case, I'd just leave the computer on sleep.