You will need to COPY any FTW file from the Old Computer and PASTE them into the My Documents/Family Tree Maker folder on the New PC. You should create that Folder. Then you install FTM2012 and it will find the FTW file(s) and open it / them and create NEW FTM files. If there are any Scrapbook items (pictures) in the Version 8 file, they will be extracted and put into a < filename > Media folder under the Family Tree Maker folder.
FTW Version 8 uses FTW as the file extension FTM2012 uses FTM
FTM2012 will find and open any existing FTW or FTM files, which is why I suggested you create that folder, Paste the file(s), and then Install.