Somewhat new to Macs. Year old aluminum macbook (not pro) with 160 gb hard drive - "Startup disk full" message - Finder says 159 gb used, 1 gb available. I am sure I could delete some software or photos but will run into same problem later. What is the best solution - put a larger hard drive in or can I use an external hard drive for additional storage (how to do this, will this impact performance). I have a 500 gb external hd for backup - can I use this?? Any suggestions greatly appreciated.