Service Account and database dbo password

I know, this wasn't set up right, but I didn't do it! The same domain account (with way too many permissions) was used to set up two SQL Server 2000 servers, the SQL services all run under that account, and that account was used to create all databases so it is the dbo of all databases. Now we need to change the password for that account and possibly disable the account.

What do I need to do to keep the servers and databases working smoothly after changing the password or disabling the account?

Thanks for any advice!