I'm not as harsh as all of the other folks; if this is a really good friend, I see no problem loaning the money, if you have it. However, based upon the last friend who you were renting to, I share some of the concern.
On the promissory note, just make sure you have clear terms and conditions, and define the payment schedule, what constitutes default, etc. Also, if you're smart, you'll have him provide something in terms of collateral, so that if he stiffs you, you're not stuck trying to collect a money judgment against a deadbeat.