How To replace hard drive

I have a desktop pc ,and has 40 gb hard drive,i want to replace this with 160 gb drive .IF i install a new one ,i would have to again install fresh windows.Is it possible to replace hard drive without installing fresh copy of windows xp

If you're going to REPLACE the hard disk - then the current 40gb hard disk means it will be disconnected - so of course, the computer will think it just doesn't exist. In that case you will need to install Windows on the new hard disk.

However, instead of replacing it, you may connect the second hard disk leaving your current hard disk connected. You will be able to access both hard disks, and that way everything on you 40gb hard disk will still be accessible - including your installation of Windows XP.