I have had success in installing all of the expansion packs onto Windows 7. Follow these steps:
First, get the latest update and install it. (
http://fallout.bethsoft.com/eng/downloads/updates.html)
1. After you put the DVD into your drive, click "Start" and then "Computer".
2. Right-click on your DVD drive
3. Click "Open in new window"
4. Right-click and copy the Fallout 3 DLC file
5. Paste it onto your Desktop
6. Right-click the DLC file
7. Click on "Properties
8. Click on the "Compatibility" tab
9. Select "Windows XP (Service Pack 2) in the "Compatibility Mode"
10. Click "Run this program as Administrator" in "Privilege Level"
11. Click "Apply", then "OK"
12. Close all open windows
13. Double-click the Fallout 3 DLC file to run it
The program should run now, and a lot quicker than when you tried to run it off the DVD. Next you need to go to the following link and download the "Fallout Mod Manager".
http://sourceforge.net/projects/fomm/
When you have it downloaded, install it and then run it.
Once it is running, click on the "Auto Sort" button. It will warn you that it is a Beta feature and may not work, but it does. It will list all of the expansion pack that are installed on your PC and in what order. You may want to make note of the order if you are one of those players who use the "player.additem" cheat feature. The item codes from the expansion packs need the two digit number associated with the expansion pack (IE. The Pitt 02). The 02 goes in place for the "xx" if the item code is listed as xx00B806.
After all of this click on the "Launch Fallout" button.
Everything should work now.
****BE WARNED...YOU WILL LOSE ALL SAVED GAMES*****
Good luck,
Stu