This should answer tell you how to boot both successfully.
First fix the mbr of XP
Fixing MBR with WindozXP CD.
1)Using partition software such as Partition MagicŪ,delete the Linux partition and distributed the free space among your existing partitions.
2)Insert your WinXP CD in your CD-ROM and enable CD-Boot in your BIOS.
3)After CD loadup process finished, you will get the Setup menu.
4)Press R to enter the Recovery Console.
5)Choose the drive where you install your windows.
6)Insert your administrator password.
7)At the console, type fixmbr
8)Press Y for all questions.
9)Reboot the Zion..oopss the PC
10)And Walla!! your MasterBootRecord has come back to normal.
Then follow the directions in this link to get Linux to work
Windoze XP - the world's most successful virus.