So i am getting my pc upgraded, with windows 7, processor from core 2 duo to Quad 2 core (or i5, if i have the money) and i was wondering, should i?

I know fallout 3 does not work as well on windows 7 than it does on windows xp, but didnt people get this type of problem fixed?

Also, if i am moving all my files and mods (along with expansions like the pitt) i only take my data folder with me (because i am backing up with a portable harddrive) and then reinstalling FO3 with the disk and then pasting the data folder, that works right?

So is this what i should do?

First thing is that since you're using a multi-core set up, remember to use the multi-core .ini fix. Ever since I did that, everything worked like it should.

Second thing is that because you're moving from XP to Win7, there are a few things that you need to keep in mind in regards to Win7. Vista and Win7 uses a diferent approach to installing and running programs, they use the "least amount of privilege" model (it's a play from the Linux playbook) and because of that, the C:\Program Files\ directory isn't the ideal place to install games because of protections in place of the Program Files directory and you don't want to elevate your user privilege every time you want to run a game. The best place I found is in the C:\Users\Public\Games directory (you'll have to make the "Games" folder) so that way you don't need to "run as administrator" everytime you play.

Third, you may have to reinstall into the new system. When I tried to just move the files from one computer to another, it didn't work. In regards to DLC expansions, I'm not sure. When I had bought DLC stuff from Bethesda (back in Oblivion days) it was tied to my computer I had purchased it from and it prevented me from installing it again when I tried to install it on my new computer. I would just get the core game installed first and then check to see if it runs proper and then add the DLC stuff and then the mods (it can make troubleshooting easier if needed).