Here's a post I made in another forum when I changed out my drive about 6 months ago. It's been working great, and is one of the best upgrades I've done:
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I Swapped out the 160GB HD with a Western Digital 320GB (5400 RPM) HD (about $140 from Newegg). Thought I'd share the process, in case anyone else is thinking about it. It really isn't that hard, even though the pictures on the net look daunting.
Googled and found several guides. Mine actually came apart with a few less screw removals than included in the guides, and it took less than half an hour to swap out the drives.
Here's a pic of the "open" book:
The hard drive is in front on the left (as you look at the picture). It's a 2.5" SATA drive ... very cute
Before I removed the internal HD, I had backed it up to a 320 GB Western Digital External Passport Drive (~ $140). I used Carbon Copy Cloner to make a bootable copy. It took about 3 hours last night to complete this part.
After I had the new drive in, I then did a "reverse-Clone," using the external drive to clone the new internal Hard Drive. All went well ... this part took less time, about 2 hours to write 120GB.
While I was at it, I upped my memory to 4 GB, getting 2 x 2GB of Corsair RAM from Newegg for about $120 (the $80 RAM kits probably work just as well).
So, now my trusty MacBook Pro has double the storage space, and is a bit snappier with it's extra RAM and faster HD.