'Indian' astrology is called Vedic Astrology. The perception is that it has very strong ties and is part of Hinduism, as a lot of the Pandits do it. This is an incorrect sterotype. I just wanted to point that out. It was devised by the Vedics who were scientists.
Now vedic astrology is when the person you go to creates a birth chart (sometimes called a teva), this is based on your date of birth to the nearist minute, your place of birth and your name. In the teva you'll see a diagram, basically a square split into 16 triangles. These depict 16 aspects of your life. Sometimes the pandits will tell you to wear certain gem stones to boost certain aspects of your life (that's why you see some people wearing pearl/ruby/saphire rings). But you can also do this by doing Paath and simran.
Usually the person you go to will look at this chart and see which aspect of your life is in trouble. He/she will look at different patterns within the diagram that affect you making different decisions eg Marriage.
You may find a lot of charlatans out there, that will make 2-3 correct diagnoses out of 10. But when it comes to the crunch time for making a life changing decision, they will make the wrong analysis. They will instill baem (sp? worry) into you.
As far as I know vedic astrology is the most accurate 'Indian' astrology there is, more so than palmistry. btw Guru Nanak had his birth chart done and the pandit started crying because he would not be able to see the wonderfull things he was to do.