I have a htc desire z running android 2.2.1.

When I go to sleep I put my phone on silent and I was wondering if it was possible to set certain people's profiles to ring out regardless of the sound setting. Eg if my sister called at 2 in the morning it would ring out but if my mate were to call me it would stay silent.

Thanks for any help.

Not aware of any free option, but you could have a look at Bedside Pro, or the ever brilliant Tasker will allow you to do this with a bit of configuration.