I did an upgrade on a 17" PowerBook a few years ago when the hard disk died.
It took some time and was pretty scary, but with patience, an anti-static wrist strap and lots of Google searches I did it. I had no further problems with my upgraded machine from that point on.
Back then, I couldn't find any one place that told me everything I needed to know - I ended up translating a web page from Japanese! 🙂
You can certainly do this kind of surgery, just be aware that it's not necessarily straightforward for the average user (like me).