I need to create a high-availablity file and printer server for a
network of windows 2000/XP workstations (approx 1000 or so) - I have
three IBM HS20 (i.e. Xeon based) blade servers and a SAN connected with
fibre for the actual storage (approx 1TB)

High-availablity is required 'cause all user files, roaming profiles,
etc. are stored on the server, and when the server drops all
workstations are unusable.

It's been planned to use a three way Windows 2003 Enterprise Server
connecting to the SAN

Anyway SAMBA solution I could look into as an alternative to Redmond