Looking at step 12 (page) of the tear down, the 2nd picture, with the color coded squares, you can see tabs/guides on the harddrive bracket that kept it secured in place. Then, from step 14 (page 2) it looks like the RAM sockets are in the way, so it does appear that you do have to pull the logic board out, at least partially, if not completely. Mac Mini Mid 2010 Teardown
Any of the intel powered macs are 64bit capable. I've got Snow Leopard installed on my mac mini, which is now 2 generations old, and when you look at the activity monitor, it shows which processes are running as 64bit processes. or, if you mean 64bit, as in able access more than 3GB of RAM, then yes, the new mac mini is 64bit, and supports up to 8GB of RAM.