Withdrawing interest or earnings of those contributions can only be withdrawn tax and penalty free by:
Having the Roth IRA account longer than 5 years and being 59 1/2 years of age.
Having the Roth IRA account longer than 5 years and spending the funds (up to $10,000) on your first house purchase.
Having the Roth IRA account longer than 5 years and having had suffered a disability.
Withdrawing from your Roth IRA for college expenses is penalty free, but not tax free. Income tax would still apply.
Knowing of these possibilities, you can plan for future expenses by saving into your retirement accounts. This should be quite attractive to young adults, like myself, since we can put money aside for our post-profrossional degrees and our first house.
If you haven't opened a Roth IRA account yet, most places do not require a minimum deposit to open an account. From what I have seen, Scottrade.com and Vanguard.com are great places to start. Scottrade offers $7 trades (the cheapest I've seen) and Vanguard has no commission on their ETF and mutual funds.