existing website + backoffice server transfer

We have an existing and fully-functional website which integrates flash and some other things. It also has a custom-created "back office." Our prior design firm is not available. We are not looking for a re-design of the website or any operational changes; we are looking for some technical assistance on transferring assets and functionality from an old server to a new server. Includes several email accounts and three domain names. Specific details and samples can be made available per request. We prefer to work with someone located in North America.