How do i install os on a dell precision 370 which has visita?

You need to put in the XP disc. Then, you have to change the boot order in the BIOS, or choose the CD/DVD drive from the boot menu.

Unless your XP disk is SP3 it doesn't have drivers for the SATA disks in your Dell (or it's even possible that you have an Adaptec RAID controller.) Download the appropriate drivers from the Dell web site, put them on a floppy disk, press F6 when booting from the XP disk and install the drivers. Then the install program will be able to see your disk(s).

SP2 also has SATA support.

I think that rather depends upon the SATA controller. A lot of people report problems installing from an SP2 disk.