I Googled the web for what to expect when I installed a new harddisk and did fresh installations of Win7 and iTunes. From what others had experienced I could risk that everything would be deleted on my iPhone and that I had to set up everything there from scratch also.
Theoretically I had this idea that after having installed Win7 with iTunes I could copy over the files that I could recover from the old disk and iTunes would have no problem "continuing" as if nothing had happened. I knew where the iTunes Music folder was, but where was the backup-files?
I found a page that explained that they were located at:
I was able to access these files on my crashed disk. And after copying them onto the new disk and checking that everything looked OK in iTunes I plugged in the iPhone.
And like magic, everything worked smoothly without any problems at all. Yet another thing that just work's with iPhone. And yes - I have learned that I must create a backup, often...