MultiBoot Vista + XP

[Unjourrajas]

Dosto mere sath ek masla hy jab main XP install kerta hun to Vista khtam ho jati hy aur jab Vista install kerta hun to XP khtam ho jati hy.

]Halan k main partition ko format b nahain kerta. aur 1 XP aur 2 vista ic waqt C: drive main mojood hain. Lekin jb pc start hota hy to koi option nahain ati.
sab sy akhir wali window khud bkhud chal perti hy.

main chahta hun k ek waqt main dono install rahain aur main apni marzi se ek window choose kr k boot karoon. Please Help Me

NOTE:
1: Partition NTFS 15GB Total space of C:\
2: XP SP2 Build 2002
3: Vista Final Edition