vCenter 4.1 Migration

Thanks all in advance for your help on this.  I'm running VMware with 2 hosts. vCenter 4.1 with sql 05 express is sitting on the 2nd host and i need to migrate it to another physical server (08 R2) along with the databases.  I have a few questions

1     Will all my VMs on the two hosts be down while i'm doing the migration?

2     I installed sql 08 express with another instance name, when i move the dbs and log files over from sql 05 to sql 08, will that cause any problems?

3     I do not know the SA password for the 2005 sql server, when i install vCenter on the standalone server, how do i go about configuring it to accept the new credentials i created for the 2008 sql account, or will it just use windows authentication to get to the dbs?