Install Windows XP over Vista Pre Installed

i'm not an expert but i think you should install the other OS in another partition... 
like yung VISTA sa C:/ yung XP sa D:/

 

since vista is already installed ....

1. go to d disk management ... shrink one of the disks - how to shrink, so u can have a new partition to install XP
2. install XP on the new partition

since vista & xp do not have the same boot manager, xp is gonna overwrite another boot loader over the vista, that is why the xp installation is the only one showing, so ...

3. reinstall vista boot loader using the vista/recovery cd, there would be an option there to search/startup repair installation - how to
4. modify vista boot loader ... just use/install EasyBCD to modify it, much easier ... EasyBCD

DONE!

kase kung fresh format dapat nakapartition HDD mo bro...maganda una install mo ang xp before vista...but still mas madaling sundin yung payo ni adrian..go for it...:)

Sir pede mo din i-try mag install ng Virtual PC sa Vista (host OS)... tapos install ka ng XP sa loob ng Virtual PC (guess OS) para pede ka mag palit-palit ng OS whenever you like to. di mo na need mag reboot to change OS and ma avoid mo boot files ng XP mag conflict sa Vista (busyversa). and kahit masira o ma-corrupt XP mo, unaffected ang Vista mo. Kung gusto mo lang po i-consider as an option. Virtual PC is free from Microsoft site.

sirs, thanks po sa mga suggestions. i had reinstalled my vista and i have partition on my disk. it is actually c: is 120 GB and d: is 99 GB. kapag sa partition d ba ako nag install ng xp, what are the next steps to do para i will choose if xp or vista o/s kapag nag boot? sir nadski, if ever naman i install virtual pc under vista o/s, ang paginstall ba ng XP is fresh copy as in start ako where i have to boot from the cd first? thanks again to all the suggestions. you are all great here!

again, after installing XP, u need to fix the corrupt vista boot loader, then after repairing the vista boot loader, u need to EDIT it to add the existing XP installation on partition D:

 

i will try to follow your instruction....hoping i could....sir adrian, cheers!!!

Thanks may natutunan na naman ako

basta install mo lang sa different partition yung XP, in your case its drive D:, then repair the vista boot loader kasi nga naoverwrite nung XP installation

after repairing the vista boot loader .... install EasyBCD on vista .... it is much easier to use if u want to add/modify another OS on the boot loader ...

just go to manage boot lader ... add the entry, choose the drive it is installedin,  which is XP on drive D:, save & ur good to go, restart & u will see the added OS on another line as an option when booting up ....

sir adrian, thank you very much. i got it finally! i have vista and xp on my lappy. many thanks to all pc techs.

that is great, glad we could help