I don't think it will work. The max ram that your computer supports is 4GB. Here are the specifications: You can use SO-DIMM memory that meets all of these criteria: PC2-5300 Unbuffered Nonparity 200-pin 667 MHz DDR2 SDRAM You can use RAM module sizes of 1 or 2 GB in each slot.
You can find the spec for your computer's memory at www.everymac.com. You'll need the model number to confirm that you have the right one when you look it up, but no Mac made in 2007 can use this RAM form factor. You can find your model number in About This Mac and System Info.
This memory is NOT designed for use in Mac hardware. Corsair's Mac memory has part numbers that begin with CMSA. Part numbers starting with CMSO (such as the number for this product) are for non-Mac hardware.
@jamken2001: No, it won't. I'm not sure which model iMac you have-there are a few different 2007 20 inch iMacs-but none will support this particular RAM upgrade. I advise you to go to crucial.com and work out which model iMac you have-once you do, you can select it from the list and see which upgrades will be compatible with your computer.
Edit: Assuming that this: http://support.apple.com/kb/SP16 is your exact iMac model, the most RAM you can use is 4GB, and you need DDR2, not DDR3. (These are just different types of RAM. DDR3 is the newer type and is faster, but can't be installed on older computers.)
You shouldn't have any problem but I would however visit Corsair's web site at www.corsair.com and check their memory guide on the front page and they will be better able to guide you on the proper selection. It should work and if different than the original ram the clock speed if faster than what you have now would drop to match the other ram.
Always check though to make sure your system calls for this speed or lower but in general the memory can be used in a lot of Mac products. 2007 model may require a different stick but I would imagine if Corsair's memory finder doesn't help, e-mail the company as they are willing to help you out.