I believe it's no use to format it since it's new (empty), alright here we go..
1) Open ur pc
2) Plug it
3) Insert your OS CD in a good reader
4) If it's WindowsXP:
a) Pick up the option to install by pressing "Enter"
b) Read the Licence Agreement, Press F8 if you agree with the
conditions.
c) specify a partition on ur new hard drive where you want the
OS.
d) If you're given any, you might wanna pick up the File System
type for ur hard drive, either "FAT32" or "NTFS", well, it's
gonna be kinda boring to come on these now, but I'd suggest
the choice with the quick formatting to "NTFS".
e) If you chose the quick formatting to a new FS, u'll have to
wait till it's done.
f) Wait for ur WindowsXP to get installed, and write down
what's asked when the dialogues pop up.
e) happy OS'ing'!
5) you forgot to close your pc!