The problem is related the error reported in the libkmod error showed in the above post.
E: libkmod: index_mm_open: major version check fail: 65537 instead of 2953311319
I don't know why but the modules provided in the folder /lib/modules/2.6.38.7-desktop-1.mga and attached to the initrd are not loaded correcly. Indeed with dracut boot i can see a lot of unknown symbol error for example when the module pata_atiixp is loaded that is used to access the disk and the related rootfs. So this is why the rootfs isn't mounted at boot time.
I tried to create an initrd without dracut the official adopted in Mageia2 with the old mkinitrd. I tried first with mkinitrd-mkinitrd command in Mageia2 and then with mkinitrd from an installation of Mageia1. Both ramdisk was built with modules pata_atiixp, ext4, ehci-hcd, ohci-hcd and others modules needed to boot.
The result was the same the kernel boot with this two initrd but when the kdm login screen is reached i can't use the keyboard and the mouse/touchpad or every hid attached to the usb ports. As work around i edited the xorg.conf file putting this line:
Option "AutoAddDevices" "False"
and manually added two InputSection one for keyboard and one for synaptics touchpad. After reboot only the keyboard was enabled and at least i was able to login and discover that the wireless module, the sound card module a lot of others are not loaded. Trying to load manually this module give the above libkmod error. Probably the same happen to the keyboard modules and mouse modules that are not loaded and this is why i was unable to use them without the xorg.conf workaround.
However i discoverd also that suspend and hibernate won't work any more with the old kernel as in Mageia1. I started this fight because i thought that with old kernel this functionality probably will come back but this was not the result. The new library of Mageia2 used to the Power Management, especially e2ram and e2disk seem to be incompatible with my hardware doesn't matter if the kernel is 2.6.38 or 3.3.8 and now another question arise:
Why i'm not able to suspend or hibernate my laptop with the old kernel ?
and
what does mean the libkmod error ?
Maybe it's related the "version magic" of the modules ? But this is very strange because it's a precompiled kernel taken from the official repository and used without problem in Mageia1.