I have the Sims 2 installed on Windows 7, but it only runs if you use compatibility mode since the game is older.
Here is the order that The Sims 2 should be installed in:
The Sims 2™ (or Sims 2 Deluxe, Sims 2 Double Deluxe or Sims 2 Holiday Edition, whichever you have)
University (or University Life Collection)
Nightlife (disregard if you have Sims 2 Deluxe or Double Deluxe)
Christmas Party Pack (US) OR Holiday Party Pack (UK)
Open for Business or Best of Business Collection
Family Fun Stuff or Fun with Pets Collection
Glamour Life Stuff
Pets (disregard if you have Fun with Pets Collection)
Happy Holiday Stuff (Disregard if you have Sims 2 Holiday Edition)
Seasons
Celebration Stuff (disregard if you have Double Deluxe)
H&M Fashion Stuff (disregard if you have Best of Business Collection)
Bon Voyage
Teen Style Stuff (disregard if you have University Life Collection)
FreeTime
Kitchen & Bath Interior Design Stuff (disregard if you have Best of Business Collection)
IKEA Home Stuff (disregard if you have University Life Collection)
Apartment Life
Mansion & Garden Stuff (disregard if you have Fun with Pets Collection)
Also, be sure to patch whenever you are prompted by the game to do so.
Source: http://help.ea.com/en/article/installation-order-for-the-sims-2/
In case you want to go back to the original neighborhoods after you've played them for a while:
Resetting Pleasantview, Strangetown or Veronaville
Make sure that The Sims 2 game isn't running.
Back up your games files. Now find the following location on your hard drive: My Documents\EA Games\The Sims 2\Neighborhoods. Right-click on the folder you are replacing, (N001 for Pleasantview, N002 for Strangetown and N003 for Veronaville) and choose 'Delete'. Click yes when asked, to confirm deletion. Find the following location on your hard drive: C:\Program Files\EA GAMES\The Sims 2\TSData\Res\UserData\Neighborhoods. (Note: This assumes you have installed the game into the default location. If you have the game installed on a drive with a different letter, then change the C:\ to the letter of the drive your game is installed on). If you look in the folder listed in step 6, you will see at least 4 folders and 1 file. The three folders we are interested in are the ones labeled N001, N002 and N003. Choose the neighborhood that you want to reset from the three folders mentioned in step 7. The neighborhoods are as follows:
N001 = Pleasantview.
N002 = Strangetown.
N003 = Veronaville.
Right-click on the folder for the neighborhood you will be resetting and choose the 'copy' option. (i.e. If you will be resetting Pleasantview then the correct folder to right-click on will be N001). Now find the following location on your hard drive: My Documents\EA Games\The Sims 2\Neighborhoods. Right-click inside a blank part of the folder listed in step 10 and select the 'paste' option, wait while the folder and files are copied over. Start your game and go to the pre-made neighborhood you have just replaced. Verify that everything has been reset.
Source: http://help.ea.com/en/article/how-to-reset-towns-in-the-sims-2/
Backing Up your Sims 2 Files:
Backup the save data in Windows XP:
Click the Start button and select My Documents. Select the EA Games folder. Right-click The Sims 2 folder and select Copy. Right-click on the folder or drive where you want to save your backup and select Paste. Make sure you re-name your copy and include 'backup' in the file name to avoid confusion. To restore your Sims 2 save games, move this folder back into the EA Games folder and select the Overwrite option when prompted.
Backup the save data in Windows Vista:
Click the Start button and select Documents. Select the EA Games folder. Right-click The Sims 2 folder and select Cut. Right-click on the folder or drive where you want to save your backup and select Paste. Make sure you re-name your copy and include 'backup' in the file name to avoid confusion. To restore your Sims 2 save games, move this folder back into the EA Games folder after re-installing the game.
Source: http://help.ea.com/en/article/backing-up-your-sims-2-files/