restoring grub loader after a windows installation.

[Mario Motta]

After having reinstalled windows xp i have lost grub loader so cannot 
dual boot anymore.
Trying to make a "void" system update using fedora core 4 disk does not 
solve the problem since even if a choosed to reinstall boot lader a 
message says:
"No kernel packages were installed on your system. Your boot lader 
configuration will not be changed"
I did the same procedure in previous fedora version with success.
How can i solve the problem now ?
A trial using linux rescue was of no help.
A quick help will be very appreciated.
tia
/mario