How to warn users that they need to enable cookies

[Calahan]

As the title says. I just spent an hour wondering why my scripts weren't working before realising that I had disabled cookies. This lead me to think of the same problem with potential users. So, how would I inform the user that their visit to my site will not work unless they enable cookies?
I am actually using sessions but they aren't being passed to the URL when using POST which is also a problem so if you want to make any suggestions there, they would also be welcomed. 🙂
I've spent some time thinking about this and I'm guessing that the script would go somewhere along the lines of an if statement but I have nothing to compare, unless I can compare a value returned from a function. Anyway, I'm rambling.

Any suggestions?

[downsize]

for sessions, see if you can turn on session.use_trans_sid .. if you use POST you will have to append the SID manually otherwise.

for checking if users have cookies enabled... perhaps send a cookie and then test for it. if you get nothing back, assume the user has not accepted the cookie.

if(strcmp($_COOKIE["cookename"], "") == 0){
  echo "error cookies must be enabled";l
}