The firm has also upgraded its e-mail system from Exchange 5.5 to Exchange 2003 to benefit from added functionality.
Pete Smith, Inmarsat head of IT, said, "The prime driver for this project was Microsoft's decision to drop support for NT4. Our Lan and e-mail applications are the core of our business systems, so we could not take a chance with them."
Smith used his own IT team and services company Datashare to carry out the migration over one weekend. The domain infrastructure was upgraded to Windows 2000 Active Directory, a new Exchange e-mail environment was rolled out and 60Gbytes of Exchange data was migrated.
Datashare provided design consultancy, implementation, post-migration support and training for Inmarsat's staff.
Before the migration, Data-share designed an upgrade plan that minimised any risks for Inmarsat. It then completed two offsite dress rehearsals with live data to calculate the exact time needed to complete the project.
Users were able to successfully log-in and access their e-mail as normal on the Monday morning after the implementation.
Smith said the roll-out had to run smoothly as none of the company's overseas offices in France, the US, the Netherlands, Dubai and Italy have their own IT staff - the IT team for the company is based in London.
He said, "Any upgrades to end-user PCs had to be automated and tested in advance. We did not lose a single PC connection."