Usual procedure when you get to a border is to go through Immigration first where you MUST make sure you get your passport stamped. They sometimes forget and then you can have trouble at the next border.
Then you go to the Aduana (Customs) where you show your passport again, plus the title and or registration papers for the vehicle. Sometimes they will come out and have a look and some even check the VIN, but not so often. They will then issue you with a sheet of paper with vehicle details, date of entry and date you have to be back out of the country. Don't lose it as you have to hand it in when you leave. Some countries have extra steps such as Chile where SAG conduct inspections for fruit and vegetables that range from extremely strict right through to the three stooges comedy. Some spray the vehicle tyres paying great attention to the outside of each tyre but not bothering with the underneath or even the inside of the tyres.

Some borders have combined border posts where you first check out of the country you are in - first Immigration and then Aduana and then move one window to the right to the Immigration and then Aduana of the next country. Sometimes you get a slip as you walk in and each window ticks one box and then there is a man collecting the slips as you drive out.

Lots of variations and sometimes there are crazy things like immigration being in a previous town and Aduana being 50 km away and down a side road (like heading out of Bolivia to Chile) or you have to pick up a bit of paper in one country for processing in the next country.
Most are very predictable and straight forward, but it pays to do some research so you don't get caught out and have to backtrack 50 miles. The central America forum on HUBB has a post on border crossings that is very comprehensive. Chile/Argentina crossings are pretty easy. Half are combined border posts and the rest are individual posts a few km apart, but sometimes a couple of hundred km apart with a huge no-mans-land - Paso Sico for instance.

Regarding the TIP - some countries have set-in-stone validity periods that are usually the same as your visa validity, but some will give you longer if you ask nicely. Argentina mostly gives 8 months TIP but only 3 months visa, but sometimes if you don't ask, they only give you 90 days.

Other thing is if you are American, Canadian or Australian, some countries operate on a payback principle and treat us as badly as our own governments treat visitors. Brazil, Bolivia, Argentina, Paraguay, Chile are examples and some of us can't just rock up to the border and be allowed in. Poms are OK though, even in Argentina. ;-)))

__________________
Tony
Click here for Travel Photos & Travel Map