hello!
can you tell me where to get a boot disk with grub supporting usb hard disks, please?

thank you

I have had alot of experience with this. I've managed to get GRUB to boot off of my San Disk USB key. It only works with motherboards that support booting from USB. As far as I can tell this is entirely dependant on the BIOS.

For instance my USB key will boot on the T30 and T41(but not T22) ThinkPads I use at work. Also It will not boot on my Asus A7N8X-Deluxe motherboard. In the cases where it would not boot it was because the BIOS did not provide an option that would allow me to boot from USB.

If you cannot boot from your boards BIOS perhaps a BIOS update will get it working for you.

in my bios usb is activated. but there is no item in the boot devices' choice for my usb hdd.

can you tell me where to get a usb-supporting grub boot manager? because my old one only detects fd0 and hd0 !

thank you

Grub doesn't care weather it is USB, IDE, SCSI, SATA, or whatever. This depends entirely on the BIOS. If your BIOS does not show USB-HDD as a boot option then it does not support booting from that device. Therefore nothing, including grub, will bot from it. The only thing you can do is flash your BIOS to the latest version supplied by your motherboard manufacturer. Then check and see if the BIOS shows USB-HDD as a boot option.

In the case of my Asus A7N8X, I called Asus and their technician told me that the board would never support booting from USB.