I forgot to tell you that I have the problem since the very moment I formatted the disk and reinstalled Windows XP Professional SP2.
After the installation, I've never been able to see the Windows folder with the explorer, neither from the tool bars in the task bar, at the bottom of the screen...
It's like it wasn't there, but actually, it is...
I have NOD 32 installed and up to date.
Previous to the reinstallation, I had the same partitions but I don't remember having that problem, I'm not sure since I didn't need to examine the folder.