I just purchased my first Mac yesterday, the 20 inch, 2.66 ghz 2 gb/ 320 hd (I think those are the specs) and I am already wishing I would have done the 24 inch with 4 gb/ 640 hd... Don't think I can return/exchange because I goofed when purchasing... so what I would like to know is how difficult is it to upgrade memory or storage? I plan on doing a lot of photoshop so I'm not sure I have enough memory or space. I'm totally computer illiterate when it comes to these terms so I'm not even sure which it is that I need more of, the memory or the storage. Is buying an external hard drive an option? If so, what do you recommend?