My wife's white 15" MacBook (early 2008) was taking forever to boot, to open a file or a webpage; she was staring at the "Rainbow Wheel of Death" more than she was using the computer. Apple genius suggested more RAM, and that the drive was maybe part of the problem, even though it tested normal.
I decided to max out the RAM to 4GB, and replace the old 120GB with a SSD 120GB. I ordered the SSD kit from iFixit.com, which included a toolkit AND a USB enclosure for an extra $10 - a great value!
First I used the USB enclosure to clone the old hard drive onto the SSD using TechTool Pro. Then I defragmented and optimized it. This whole process took many hours because the computer was running so slowly, but I think it was worth it.
The instructions & pictures were very clear, but this model is SO easy to replace the RAM and drive on - remove the battery and three screws.
I replaced just the hard drive first, and booted up. I immediately noticed a big difference - it took seconds to do what used to take minutes. Then I installed the RAM, and this computer works at least as well as it did brand new!
Thinking about it, I probably should have replaced the RAM first, THEN cloned and optimized the SSD -- it probably would have been a much faster process. By running Activity Monitor, I found that having only 1GB meant that running OSX 10.6 and just one program maxed the RAM out, forcing it to use virtual (disk) RAM. 4GB makes a HUGE difference.