I need to know is it good choice to upgrade to vista 64bit ?
Yup. More RAM available, better use of Quads
Can I have my current raid configuration for vista 64bit ?
Yup. RAID didnt disappear when Vista got released
Is it possible to test vista 64bit in another partition while i have vista 32bit ?
Yup, though you may see a few emulation probs when running 32bit / 64 bit OS's on some lesser developed applications