NT 4 Workgroup Upgrade to Domain

What is the best course of action to upgrade a NT 4.0 workgroup with win 98 and win 2000 workstations to a domain environment? Is it better to move to win 2000 domain with active directory? There are 25 ws and will soon expand to 60 in 3-4 months. Are there docs with details of how to do this with minimal downtime since we are 24/7?