I see you've already got quite a few replies, but here goes:
I spent 10 weeks in India during the fall of 2005 working on a steel mill control upgrade.
Are you being paid by a western (US, UK, Canada, Australia, Germany, etc.) or a firm local to the area (India, Malaysia, Bangladesh, China, etc.)? If you're being paid by a local firm, either get paid ahead of time or via an escrow account in a western bank. On a business level, that part of the world does not have the same concept of financial obligations we do.
Is the customer site remote from major public transportation? We could not travel freely, or go home without the assistance of the end customer. It never became an issue, but it did make me nervous at times.
I was mildly sick most of the time because I was adventurous in trying new foods. Pay attention to food preparation. It's best to eat food that has to be immediately cooked in front of you. Most places do not have refrigeration, and sanitary conditions are terrible.
Speaking of sanitary conditions, bring hand sanitizer and pepto. Your hotel should have toilet paper; steal some rolls to carry with you. The VAST majority of places will not have toilet paper, seated toilets (just holes in the floor), or soap.
Only drink sealed bottled water. Even the locals boil their drinking water. You can become deathly ill from drinking the local water.
Get immunized and get malaria drugs. The malaria drugs are hell on the liver long-term, but they beat getting malaria and having debilitating spells for life. Also, long pants and long sleaved shirts that breathe well will expose less of your skin to mosquitoes.
It will also be VERY hot or raining HEAVILY.
If you're going to a dry state (I was in Gujarat, which was dry), and you drink at all, get a 'tourist alcohol license'. They are easy to get with a small bribe. You can then buy alcohol at special state run stores.
All that being said, if you're an adventurous person you will enjoy it. The food is delicious, the people are very friendly, the accommodations are usually VERY luxurious and inexpensive, and it is an amazing place to see. Make sure you don't have to drive yourself anywhere; there are only mild traffic suggestions, not many enforced traffic laws. You can also get very high quality jewelry, clothing, and rugs pretty darned cheap. Just be aware of how much you can bring back without paying duties.