Here is the general rule that you should follow: disclose, disclose, disclose. If you don't disclose, and your law school later discovers the disciplinary issue, you can be dismissed from law school. If they discover it after graduation, your degree can be revoked and you can be disbarred. I'm not making this up, check with your state's bar association.
Perhaps you already know this, but before you can be admitted to the bar you will have to acquire a positive Moral Character & Fitness determination from your state's bar. The process is essentially a detailed background check, and you will be required to disclose any and all instances of academic/legal probation. The bar will quickly figure out that you lied to your law school, and you will rue the day you failed to disclose. As you will learn in law school, when it comes to state bar admissions the cover up is often worse than the crime. Disclosure must be full and frank, making excuses and playing word games will not be tolerated. It is imperitive that you disclose the good, the bad, and especially the ugly. Anything involving drugs (yes, even pot) is taken very, very seriously.
I'm going to assume that you're friends who think this is no big deal are not law students or lawyers. Don't listen to them. I don't know how much disclosure will harm your chances of admission, but failure to disclose (which will be treated as a LIE by the state bar) will certainly hurt you.
Now, don't lose heart. I don't know what state you're in, but you're not the first person who has applied to law school with such issues. People here in CA do get admitted to law school and the bar with such isues, provided that they demonstrate that they have learned from their mistakes, remain squeeky clean, and are fully, 100% honest about their bad behavior. You should contact your state bar (or whatever state you want to live in) and ask them about their policies. They may have a program you need to follow to gain admission.
I hope this helps, and good luck!