OS X :: How To Redirect Webpages

I'm having trouble with people at my workplace spending too much time on non-work related websites (MySpace, YouTube, etc...). Ideally, I'd like to be able to do the following, but of course, this is a Mac. I would need it to work for both Safari and Firefox

code:Prank your friends by redirecting there favourite site into something there not expecting! NOTE: Heres the written tutorial because i forogot to put audio onto the video... ;( Written Tutorial: STEP 1. Find a website that your friend would NOT like to go to... STEP 2. Go to the site:

[URL] STEP 3. Type in the URL you would like to direct in the "Enter a host name for Forward DNS Lookup:" box STEP 4. Press look it up, and copy the IP address down. STEP 5. Click on "Start" ---> "Run" and type in "notepad cwindowssystem32driversetchosts" STEP 6. On the last line paste the ip address, press tab and type in the URL your friend will visit STEP 7. Save and test Once he goes to the website he wishes, it will redirect into the website you set it to Hope this prank goes well!

Failing that, is there a simple way of just blocking websites from the OS and only allowing administrator access to bypass these?