Calm down: this is an happy-ending story.
I've recently upgraded my Archlinux machine to linux kernel 3.0.
After that, obviously, I haven't be able to boot my machine because Grub claim the error 15 (file not found).
Anyway the workaround is easy. The problem is in the naming convention for the kernel images. It is different in the new release respect of the old one: the vmlinuz2XX is now vmlinuz-linux and the initrd-2.XX.img is now initramfs-linux.img.
This post could be useful.
So when the Grub menu shows up you can press the 'e' key and edit the item to change the name of files. After, boot the system by hitting the 'b' key.
...and remember to properly reconfigure Grub (or (Grub2)[https://wiki.archlinux.org/index.php/GRUB2]) before restart linux again... this is a reminder for myself, obviously.
