I went to store and all Duo Core machines there are running Home Permium 32 bit. I have a 2.13 GHz 2 duo and am confused if I should ask for 64 bit version.

One note! If you get Home Premium you will no longer have a Fax Console. It only comes with Ultimate and maybe Business. I used to fax from inside documents but when I did the upgrade it no longer was possible, and to top it off Vista would not recognize or let me add the Fax printer that is in my Brother MFC-420CN.