Hello,
The content database should not be very hard to reconfigure. In the Central Admin, in the DB section where you can chose to configure connections to content databases, you can add your new content database on the new machine as another content database and then chose to connect the site(s) that you want to use.
What kind of errors do you get when you try to change the content database? Have you made sure that the account used to connect to the Databases has enough rights on the new SQL server? There is a section in the Windows SharePoint Administrators guide that lists scripts how you change this properly (it is under the section Changing Application pool identity for a virtual server, scroll down and you will see how to change the db rights in a proper way)
Also in a previous post you say that the sites points to the old server, are you using DNS resolution for the sites? then you will have to change the DNS entries aswell to point to the new server.
Regards,
Thomas