Fedora 4 test 3 on USB Hard Disk;

[Mirco Beaker]

Hello there everybody,
I have finally mamged to install Fedora 4 3 test on my secondary USB 
hard disk.
During setup, Anaconda detected my usb hard disk and partitioned it as 
usual.
I decided to install GRUB on the MBR on my primary internal Hard disk 
with Windows XP installed (for now),
Once the installation was completed, I rebooted hoping to have as first 
screen GRUB and all the usual options I would get with two internal Hard 
drives.
UNFORTUNATELY, there was no grub and the system just procedeed booting 
Windows XP.
I set up the BIOS of my DELL OPTIPLEX GX270 to be able to boot from USB 
emulation therefore the external hard disk but nothing happened.
Is anybody able to help me here?

Mirco