Minimum hardware/system to render HD files

[animal]

As we're looking at 3000-4500 $ Canadian to render a 100-120 minute 
film (1920X1080 pixel Tiffs at 24fps) onto HD 1080 60i for a film 
festival - what kind of mac & hard drives would we need to do the 
rendering ourselves and would it be possible to then submit the file to 
the HD place?  We currently have an Emac 700 and an older G4 400.  Is 
rendering even possible on either of these machines or would it just 
take an awfully long time?

Thanks
Lynn