Yes, use a 64 bit OS but make sure you use 32 bit Domino.
You can move the required databases over or you could install from scratch since the install time is fairly short providing you know what LDAP server (if you're using LDAP) you are using, bind accounts etc.
There are various IBM Technotes available and guides of how to achieve this.
You can also find the part numbers you need to down load here http://www-01.ibm.com/support/docview.wss?rs=477&uid=swg24031295
You'll need to go to http://www-933.ibm.com/support/fixcentral/
and down load all the latest patches for the Community server and install them once you have got the base server set up.