I just checked it out and you can make encrypted disk images quite easily.
- Open disk Utility
- choose new image
- give it a name and under encryption choose AES-128
- Choose a size and imput the password
When the image is open you can put stuff into it. Close it and it locks and to open it again just input the password again.
interesting. is that feature part of 10.5 only? or has it been there? anyways, thx for the info!