I absolutely hate it when I lose a screw or what about when you accidentally strip a screw and now its stuck in the case stripped.  This is never fun, so I suggest if your going to be doing the work, you should have some tools as opposed to having every little piece of hardware that some geek (me?...) may say you need.  But definitely some tools if not a whole set that satifies you, just saying you may not need it.  You could purchase a PC Tool Kit, or you could just have what I list below.  Now I'm not saying you wont need the tools, but if your short a few bucks you may not want to spend the money on a new set.  Theres two types of tools you will need when working on your PC, either software or hardware tools.

Safety is very important when attempting to assemble a new PC or replace a piece of hardware.  If you're ready to take things in your own hands and try to fix your personal computer by replacing a piece of hardware or setting up an entire new rig, it is a bit easier than you may think. But before we jump too far ahead we should spend some time learning how to handle the hardware accordingly.

These safety precautions are intended for replacing hardware or putting together an entire new computer only.  If your product has failed, you should send it back to the original manufacturer for warranty, do NOT attempt to open up any hardware or peripheral, send them back, or dispose of them accordingly.

If your PC looks like this you should definitely dust it out.  Unfortunately this PC had not been dusted out in years so after installing a NIC Card to connect the PC to the users network, i decided to give it a cleaning.  Look at how the dust has embedded itself in cracks that dusting with only a compressed gas duster did not clean up.