Online or casino? In a casino you aren't going to find a cheap enough game to play craps smart with only $100. The best bet in almost every casino is pass line with max odds. But that means you're betting at least $20 and sometimes $50 (depending on what odds they let you lay). If it's online, who knows, there might be places that let you play $1 pass line bet and 100X odds, which would be sweet. You always want to play as little as you can on the pass line and then as much as you can afford on odds behind it. If you had more money you would be thinking about playing come bets and laying odds on those too. Lowers the house edge even further but increases variance. I craps. Check out this page:

http://wizardofodds.com/craps