i share a computer with my brother and sister, we all ahve our own file like our own log in , When i download something in my file it always go to there file how do i make it so all the things i downlaod in my file it dosent got to there file?

Do you mean that when you install a program in your account, they get shortcuts to it on their Desktops and Start Menus?

Both accounts have their own My Documents, you can store your downloads there.

If you really want 2 whole different & independent systems on one computer, you have to split up your hdd (partitionate), then install your XP on each partition once. Then you type 'msconfig' in the 'run' window (in start menu). There you can change the boot-appearing order of the two systems on startup. If you boot tough, the two systems will have the same name ('windows xp home/pro edition') which is confusing which one is yours. You can solve that by searching the systems boot.ini file (the one of the first system you have installed xp on*). You open it in notepad, and you can change the names of the OS of both partitions. You save it, and if you then boot your computer, you will first have the choise between the two systems with the names you gave them by yourselves, before windows boots up.

*It's easy to do, but you have to search a bit to set it in the right order. If you don't do it right you won't have the choice between the two systems anymore, and one of the two systems will boot up directly. Then you have to reformat both partitions and start all over again
(i've done all this once, and i had this mistake, that's why i warn you for it... But i'm glad i have 2 totally seperated systems in one now, it's worth the sweat. But if you are not familiar with computers, forget this all before you make it a mess)

EDIT: don't forget that me nor this forum is responsible for any caused damage to your computer