onnetz: what hair do you use in your scenes? FWIW even though I do most of my rendering in Carrara 5 Pro (rendering in P6 is tooooooooo sloooooooooooow) but even there I still find that the more complex the hair the slower the render times.

Likewise your lighting setup - try looking up references from the photography guys on lighting setups with main, fill and back lights only as some of the free & bought lightsets can load in 20 or more light sources.

Also, when changing from one light rig to another, use the python script to delete all lights as they often 'hang around' clogging things up when you think you've loaded a new set.

Other than that and as much ram as your motherboard can take...time to upgrade I'm afraid...

Hope the suggestions help...M