thanks for your valuable suggestion. However, I just discovered that the preinstalled version of Win 7 64bit is already set up in four primary partitions: system, data, recovery and HP (Hewlett-Packard) tools.
I think it is not possible to create more than four primary partitions. Does it mean that I can't perform a dual install at all? Or is there a way out of this scam?
As a side note, I ask myself whether they used up all four primary partitions on purpose, just to force people to use their cozy 64bit system