Normally in the most cases you can do the follow steps
1) Start a fully Admin level Backup for all accounts
2) Install the new server, with CentOS 5.2 (or 5.3, not sure if its supported already by Directadmin).
3) Put your current server offline
4) Add the IPs to the new box
5) Import backups and you're done.
Or if you just have 1 box, just start backups to USB-drive or external location, when done reinstall server, add IPs, import backup.
If you need help contact me through PM.