Is it OK to build a new 4.1 VC install on a 64 bit server and create a 64 bit DSN to connect to the original VC database which will not be touched during the upgrade or do I need to upgrade the database to run VC 4.1?
The install of vCenter 4.1 will have an upgrade to the DB schema, so during the install when you choose to use an existing DB, that is when the upgrade will happen.
Also, if you are starting off on a new new Host OS, and installing vCenter 4.1, you will have to copy the SSL directory out of your old 2.5 instance.
Also, make sure you have a good backup of your DB before you start.