I'm afraid I have no clue how all this would work on a Mac - I am a Windoze user. If anyone plays Sims 2 on Mac and would like to write a tutorial please contact me!
Take as a given that your game will run more smoothly if you have loads of room on the C drive, even if you installed it on the F drive! This is because, while running, it uses lots of temporary space on the C drive, AS WELL as storing loads of stuff in the My Documents folder.
Because Sims 2, as well as SimCity 4, and many other games, puts all downloads and a great deal of information into the My Documents folder, this can become very large.
In Windows, the My Documents folder is by default on the C or home drive. As the C drive is also where many other programs install themselves, it can become cluttered, and that can slow your game down or make other programs run more slowly. EA tell us to defrag regularly and that helps a little. There is another thing you can do.
As hard drives and computers get larger, many of us have multiple partitions or "virtual drives". If you have, you will see more drive letters in the My Computer view.
If you have, then you can move your whole My Documents folder off your C drive because it has a pointer which can be reset. If you have a computer like mine, with several drives (or one hard drive divided into several virtual drives) this is a very good thing.
Go into My Computer
from your desktop icon.
Here is a screen shot of my computer. This is using Windows 2000. You can see that I have one 20 - Gig hard drive and one 120 Gig one, which are divided up as you can see into C, E, F, G and H. (Please ignore the others - those are network drives i.e. not on my computer physically.) If you don't understand how to set up the virtual drives, I'm afraid you will have to ask your system administrator or local computer expert. I don't set my own up, it is done for me by my blessedly geeky sons! but I believe it is part of the process of installing a new hard drive.
OK. From the view of My Computer, find My Documents. To do this,
use the 
"up a folder" button on the top of the
window. That should take you to your Desktop. Right-click on My Computer and
select Properties.
On the tab that is called Target, you can set where my My Documents folder is. Initially it is set to point to the C drive but it can be anywhere on your computer. Reset yours to whichever drive suits you - make sure it's somewhere there is lots of space!
I simply reset the drive letter on mine to the F drive...
This frees up a LOT of space on the C drive! Of course your F drive is now relatively full...