Hi
If this this 1.8GHz cpu is a socket 478 version max speed available 3.4GHz
from 2002 (but only second hand parts available nowdays)
If a Socket 423 version no point in proceeding get a new motherboard
http://en.wikipedia.org/wiki/Pentium_4
use CPU-Z to find out what socket this Pentium 4 is
and motherboard manual for max speed cpu it supports.
Unless hard disk has been replaced it is living on borrowed time so will need replacing but new PATA hard disks are rare nowdays so more expensive than SATA
what AGP version is that motherboard ?
what resolution is screen (is it CRT or LCD) ?
low resolution screen can be driven by lower spec graphics card than modern high resolution screen
This old P 4 is OK for office, internet...