yes you can but it's pointless with 2 GB RAM
why do you want to run 64bit windows on such old system in the first place?for your information 64bit is required only if you have 4gb or more ram.for less than 4gb ram best option is to run 32bit windows.
Yes, 4GB RAM is recommended for running 64-bit Windows indeed. Now I understand the slow response of a friend's core i3 laptop running windows 7 x64 on 2GB RAM... anyways, does it make considerable difference running 64-bit on higher RAM?