My computer has a HDD:
+ C is primary partition. It has been installed XP.
+ D,E is logical partition.
+ The last is undefined partition (6G) to install Linux
After installing Linux, on undefined partition with GRUB, GRUB was installed on the same Partition of Linux. I can't boot Linux.
Please Help me
Thanks

Distro? And what instructions did you follow?

Probably installed Grub only on the Linux partition.
Now you need to tell XP about the Linux boot partition.
What you need to do is boot from a live linux cd and use dd to dump the first sector of the linux partition to a file and then copy it over to the XP partition and then edit XP's boot.ini file to add an entry to use said file to boot the linux partition, etc...
You can do a search here for other posts on how to do this.


Or you can install Grub to the MBR and use it to handle the booting of Linux and XP.
The only negative with this is that if you decide to remove Linux you will need to reset the MBR to get XP to boot.
This is minor tho.