How to extract 001 files?
Joining with WinRAR
Open the first file of the archive (name.001) with WinRAR by double clicking on it in the Windows Explorer. Normally a window will appear asking you which program should be used to open the 001 file (this is because Windows might not know which programs are capable of opening 001 files). So select WinRAR in that window. If WinRAR isn't listed, press the 'Browse' button and navigate to the WinRAR folder on your computer (probably C:\Program Files\WinRAR) and select WinRAR. Finally press the 'OK' button.
Now there are two possibilities:
1) WinRAR is able to open the file successfully. Now you can extract the archive in the same way you would extract normal RAR archives, as explained in the WinRAR tutorial.
2) WinRAR is unable to open the archive and you get the following error message:
In that case WinRAR is unable to join the files, so we have to try the programs 7-Zip or HJSplit. Both programs are free and will be explained below.
To the next chapter: Joining with 7-Zip