I don't wash my nappies with other stuff but you certainly can, Dgirl. I just find that I usually have a full load once I am ready to wash the nappies anyway (I only have a small washing machine).
I've only ever washed in cold water and haven't had any probs with the nappies being stinky.
Just make sure that you regularly dry the nappies outside in the sun and fresh air to get those nice UV rays