Hi,
I am not sure if i get you right.. but you have purchased a new server with exactly the same hardware ?? in that case a hard drive swap may be the easiest and best solution.
Migrating data and roles to a new server is a lot more involved and you can be thankful that you have not already installed exchange as this could have caused all sort of issues if you did not do the migration successfully.
A question though? how have you setup the hard drives on the new box ? it may be wise to blow away the config and re-evaluate the best config for the new system prior to installing exchange as running exchange and AD on the same box will be quite resource intensive depending on the number of users on the network and what they will be doing ?? i assume the box is also used a File/Print Server. My suggestion first would be to leave the roles of DHCP and DNS at the least if not File/Print on the old server and look at migrating the roles of AD on to the new box with exchange on the new box. You could always log onto the box via remote console or get yourself USB keyboards/mouse to resolve your issues.
Either way you have a new box now so put it to good use and improve your network performance while maintaining some kind of redundancy on your network .
You will need to follow the following steps.
1. Setup AD on the new box and ensure replication.
2. Move the fsmo roles from the old active directory server to the new server ( this can be done via ntdsutils or via the active directory snapins) there are 5 roles you would need to move to make the new server the PDC , infrastructure master, schema master ..etc.. but you can always share the roles if you wish .
3. Do not shut down the old box but ensure it is running and check for replication .. use repadmin here.
check the active directory sites and services snapins and you should have both servers setup with replications policies between both boxes.
Keep this running for atleast 24 hours and if you do not wish to utilise the old server then once you ensure everything is ok .. checking the logs .. you can turn it off and check again .. if all ok .. remove it from the AD site .
I still would recommend using the old server since you have many uses of the box..
I hope this answers your question ..briefly
Ali Daher