At the end of this step, STOP. Go back and choose the guide for Logic Board replacement. That will get you to the point where you have the main board disconnected and removed from the computer. Then come back here and pick up at the next step.
I found it impossible to lift the speaker out without breaking the plastic mounting pin. All I can say is don't worry about it if it happens. When I put it back and tightened the screw, it seemed solidly in place.
This is an old post, but in case anyone has the same questions:
-Is there a way to add an SSD to the mix? Much like the video for the late 2011 iMac - putting a second SSD drive behind the optical drive?
The hard drive can be replaced with an SSD. There is another guide that shows how to replace the DVD drive with a hard drive.
-Or should I just replace the HD with a smaller SSD and use external storage for iTunes etc.?
That is what I did. I moved my iTunes library to an external drive so a smaller hard drive would be OK.
-Also, with this iMac being so limited in RAM (4GB Max, yes?) Is it worth spending the money and time to upgrade the HD to SSD?
You can actually go to 6GB of RAM. Go to macsales.com and find the RAM options for your model. You should see an option to put in a 4GB and 2GB stick. I have this is my mid-2007 20" iMac. As far as the SSD, I think it makes a huge difference. Startup time went from 1.5 min to 30 seconds. Launching apps is way faster. I am happy I did the upgrade.
I just did this upgrade on my mid-2007 20" iMac. Not too difficult if you take your time. I replaced the 320GB HD with a Crucial MX100 256GB solid state drive. I used the Newer Technology AdaptaDrive 2.5" to 3.5" Drive Converter Bracket and it fit everything perfectly. I would recommend this upgrade for anyone willing to open this machine up. There is a huge difference. My startup time (in Yosemite) went from a minute and a half to thirty seconds. Launching apps is significantly faster. Very worth the time and money.
Note that just below where you are working is the PRAM battery. If you have never replaced this, now is a good time so you won't have to open the machine up again in the near future. The battery is a CR2032.