also, just a suggestion prior to your upgrade. you MAY want to think about going ahead and upgrading the current installation to 4.0 SP5a, assuming you're using BESX (otherwise, whatever the latest SP-level is).
as for the rest of the move, all you will need to do is install the SAME version of BES on the new hardware, along with all service packs from the one you're moving from. you will need to keep the following FOUR items the same: BES service account, BES instance name (CORPBES11, etc), the SRP identifier, and the SRP auth key.
also, and most importantly, in the process of building this new server, DO NOT start the BES application or services! at the end of EVERY installation, uncheck the box that states to start the services. if it prompts you to reboot the server, BEFORE YOU DO SO, go to Windows Services and set EVERY BlackBerry service to MANUAL. if it never prompts you to reboot, then go ahead and set these services to manual ANYHOW (until the migration has been completed). Under NO circumstances do you want to start these services with the same SRP ID, etc. while the current production server is running - it will IMMEDIATELY disable your SRP and you'll have to contact RIM to have it re-enabled.
just a friendly warning...