Just migrated our two sharepoint sites to the new server. After a bit of digging I found an easy way to do it.
Both our servers are on the same domain so I didn't need to manually create new user details. So here is what I did:
1) On the new server create a new web site
2) upgrade this site to have sharepoint services installed (don't visit the site for now as it will ask for a new template)
3) On the old server run this command (changing the details that suit you)
smigrate -w http://sdp.dalegroup.net -f C:\inetpub\sdp.fwp -u dalegroup\administrator -pw *
4) Copy the fwp files that are created to the new server (I had a few as the sites were large)
5) On the new server run this command (changing the details that suit you)
smigrate -r -w http://sdp.dalegroup.net -f C:\inetpub\sdp.fwp -u dalegroup\administrator -pw *
6) Login and test your site, you will need to add the users back into sharepoint.
7) Update DNS etc
8) Shutdown the old sharepoint server