Cell value changes another cell or displays a notification

Hello all, I am a newbie here. I have used the site many times without posting, here is my first post.

I have a time card that I insert a week number (cell B2) and it generates the dates for that paticular week. What I would like to do is a function that when I insert say, week 40 and one day of that week would be 10/5/2010. I would like a noticifation box or sometype of display saying that this paticular day is a holiday.

OR....... have a paticular cell change color say yellow.

The reason for this is that I sometimes forget some of the holidays on my time card. I have attached a sample of my timecard. Thanks for any help......