Dual boot concerns

Good Day!
Anyone can help me regarding dual boot. My os is win xp sp3 then i want to have another OS like vista home/ultimate. I already partition my hard disk.Whats the next step Il do.?
i have vista home 32 ,i already experienced when i installed the vista in my second partition my previous OS is win xp sp3 is gone and all my files was lost. vista overwrite all. any idea on how to duol boot xp to and
vista?
Lastly,Is it possible my vista home 32 is pre-installed by my ecs laptop it is free when i bought this one. then this vista has no bootloader based what i observed it will directly installed not like vista ultimate you can choose where to setup i mean the partition can be seen, in my case the primary and secondary partition cannot coz my vista home have no options. So i can dual boot my win xp sp3 and vista home 32 or not?