mexico help
I go to Mexico about every three weeks. You don't need to exchange your money for peso's, but as the other response noted, DO NOT FLASH CASH!!! They don't f@%& around down there.
If you cannot tell what is fake and what is legit, just stay home and save your money. If you are planning on going to Tijuana for your purchase, you will find more fakes than legit gear unless you know where to go. 90% of the pharmacies will carry fake Norandren, and all of their prices will be higher than a Vet store. If you want to stay a little further from trouble (ie: cops and arrests), when you cross the border and get to where the taxi drivers will be bugging you (you cannot miss it, trust me) Turn to your right, and head towards the ABC bus terminal. The bus terminal is only a couple minute walk. Go into the terminal and ask for the next bus to Ensenada. It will be about an hour and 10 minute ride to ensenada, and the cost is about $7 each way. you will find alot more real gear there, but still try to stick to the Vet stores.
If you choose to stay in Tijuana, a taxi down town will run you $5, but since the Sept 11th ordeal the tourism is down and you can get a ride downtown for $4 (also the street girls have dropped their price to $15 for whatever you want. at least that is what I HEAR!). It took me about 7 trips to find a couple legit places, and that is the only places I go now. If you cannot find one, you can still get your gear, you just need to go from store to store picking out the real stuff, and leaving the fakes for the guys who don't take the time to learn what is real.