Use the Windows RE (Repair Environment) under Window 7/Vista to repair and replace missing or damaged files. For XP users, you can re-install XP without erasing applications or settings, or use the XP Recovery Console to fix some problems. Pick the OS solution below.
Using Windows RE for Windows 7/Vista/Server 2008
For detailed instructions with screen shots, go to Using System Restore 7/Vista/2008, or use the brief summary here:
You'll need the Windows installation DVD. Note that many OEM manufactures leave out the installation DVD, which has to be purchased separately, or they only include a limited restore DVD that just erases the system and starts over (often a poor choice). All retail copies of Windows include this bootable DVD.
Insert the Windows DVD and reboot the system. Assuming the BIOS defaults to booting from the DVD (usually the default) then select the language. Next click on Repair your computer. A list of Windows installations should appear. Select your installation (typically there will only be one).
A list of recovery options will appear including an automatic repair function, restore from a previous system restore point, restore the computer from a backup (assuming one is available), run the memory diagnostic tool, or go to a command prompt (for advanced users).
Using Windows Recovery for XP
For detailed instructions with screen shots, go to Using System
As a reminder, not all hal.dll files are the same and if the system was using a different version or one provided by the PC manufacturer that is different than the one you copied, it may cause odd behavior and/or hang at a later point.