Upgrade path 5.0.12 on NT40SP6a to 6.5.1 on Win2003

Dear colleagues,We have at the moment Domino server 5.0.12 running on Windows NT 4.0 SP6a server. We plan to buy a new hardware and migrate to Domino 6.5.1 on Windows server 2003. Can it be done in one step? Or should we migrate to Domino 6.5.1 on Windows server 2000 first and then upgrade to Windows server 2003? May be there are another considerations?

Thank you.