XP or Vista?

my assembled pc is Core2duo 2.2 w/ 2gb of RAM DDR2 and 160 HDD cap. what is the best operating system that you can suggest? if i intend to use such adobe photoshop cs2,revit8.1,autocad2008 will it be able to work on Vista? one more thing is what anti virus is best if you dont have internet connection yet?