Hi,

Just downloaded the game, I'm so happy, haven't played this in 15 years. However I was hoping this version of the game would give me access to the Chaos, Eldar and 'Nid units.
Any idea if/how that can be done?

There's only Imperium and Orks. Chaos, Eldar and 'Nids were planned for expansions but the expansions were never made.