Is the CD scratched or dirty?
If so rub clean with a soft cloth (cotton T-Shirts work well) and try again.
Have you tried manually installing it using the "Setup.exe" directly off the CD?
To do this click "Start" and then "Run" and type "cd:\setup.exe" - replace cd with the letter of your CD/DVD-ROM Drive.
Can you install other software?
If not you may have a problem with your CD/DVD Drives setting.
If this doesn't work, you will need to post some more details for anyone to be able to help you much more. E.g. What version of Half-Life (Original, Game of the Year, Generations) and your basic system specs.
