Ok, you redownloaded them..did you try installing them? Cause if you try to install 1.51 over BF2142 1.51 it will throw up errors, so you have to completely uninstall it. There is another method that involves a registry edit but (and this is going to sound rude) I don't think that you are capable of it from the sound of things.
Delete all versions of BF2142 patches and FirstStrike versions. This is to make sure you do EXACTLY what I tell you and have the correct files. Removing the old versions means you shouldn't be able to use the wrong file.
uninstall First Strike and Battlefield 2142.
Reinstall BF2142.
Download and install BF2142 1.50 from here:
http://www.gamershell.com/download_26858.shtml
Download and install BF2142 1.51 from here:
http://www.gamershell.com/download_69646.shtml
Now, run BF2142 and make sure it works. This will also update Punkbuster for you.
Download FirstStrike 1.50 from here:
http://www.woodat.com/builds/FirstStrike_v1.5.exe
Run and install FirstStrike. During installation a window will pop up asking you to install the FirstStrike launcher. Do not click to install this until all features of the main FirstStrike program have installed.
With everything installed, run the first strike updater/launcher program. It should look for and download a patch for you automatically.
With the patches complete, run the game. If you still experience problems, just go back through this thread to my previous post on how to swap out the .exe files and change your resolution setting.
Bite my shiny metal Tie Fighter!

