Believe it or not, there is a fine line between conducting a fun, hopeful office lottery pool and gambling. Make sure that if you conduct an office pool, have each contributing member throw in the same amount of money, and then have a group leader pool the money and go purchase the tickets. DO NOT purchase tickets first, pool the tickets, and then collect money. Oddly enough, under the laws of Missouri, that could be considered illegal gambling as it is viewed as a second game of chance. Be wary.
I was recently interviewed by the local CBS affiliate KOLR10, pertaining to conducting legal office pools.
Good luck!