How to reinstall a missing file in XP

I was re-installing XP and some files could not be written from the CD to the folder so I retried and eventually I pressed F3 to cancel. Now when I restart the computer I get the following message: “Windows could not start because the following file is missing or corrupt \system32\hal.dll Please re-install a copy of the above file.
How do I re-install the file and how can I get my computer to boot from the CD ROM so I can re-install Windows without getting this error message.