Help with list validation please

I'm trying to do a validation in one of our list. Basically, I have a drop down box with 5 choices (let's say choice1 to choice5). If choice2 OR choice3 is choosen, I'd like to have a mandatory field (simple line of text). I can't come up with the correct syntax to make it work. Here's something not working...

=IF(OR([coloumn1]="choice2";[coloumn1]="choice3");AND([coloumn2]<>"";TRUE;FALSE))

Thanks in advance for the help!