Hi 45rpm:
Here's the process I used for downloading and installing overwatch. I don't know how far you've gotten, so I'm starting from the beginning. Let me know if anything doesn't make sense.
1) You need to download two files to install overwatch:
Resource.cfg (http://www.modthesims.info/wiki.php?title=Game_Help:Installing_Sims_3_Package_Files/Setup_and_Files)
NRaas_Overwatch_V25.zip (http://www.the-isz.com/nraas/index.php?topic=394.0)
To keep things simple, I downloaded both files to a folder on my desktop (you can name it anything) and unzipped overwatch to this same folder. When overwatch is unzipped, you'll see a file called NRaas_Overwatch.package. This is the file you'll need for the game.
2) Go to Documents/Electronic Arts/The Sims 3 and create a new folder called Mods
3) Copy and paste Resource.cfg to the Mods folder
4) Create a folder called Packages in the Mods folder
5) Open the Packages folder and copy and paste NRaas_Overwatch.package here
6) That's it. When you load a game file, you'll see a notice that overwatch has been installed. It will immediately start working on its own.
There are some screen shots at http://forum.thesims3.com/jforum/posts/list/217955.page if you want to see what the folder structure looks like.
