A trip to India involves a pile of admin and form filling. Begin the process well in advance, as it takes a long time - often longer than promised.
A visa is obligatory if you want to travel to Inda. Most countries are required to follow the same steps. You need to apply for a visa in advance and your passport must be valid for at least 6 months after your return date. It must also have 3 clear pages, two of which must be a double page.
You must attach a copy of your passport to your application, along with two ID photos. Make sure you fill out the form correctly. The application procedure is long and arduous - be patient! First of all you'll need to connect to VFS English's website. You need to fill out a form, which takes about 30 minutes. Once printed and signed, you need to send it off by recorded delivery with delivery receipt. Expect to wait at least 2 to 3 weeks for a 6 month tourist visa. At first glance, the process seems tedious, so you may decide to go through a specialist travel agency. It will cost you, but it saves a lot hassle.
As for vaccinations, they're not obligatory, but you would be wise to get innoculated against Yellow Fever, Typhoid, Hepatitis A, Meningitis and Rabies.
Unless you're from Luxembourg, you won't be able to get a visa on arrival. If you plan to visit certain regions, including Arunachal Pradesh, Nagaland, Sikkim and Ladakh, you'll need to get a special 'Protected Area' permit. You'll need to apply several weeks in advance and can do so in a local DC (District Collector) office. Expect to fill out a ton of paperwork and remember that patience is a virtue.
Finally, a word about vehicle hire. Normally, your driver's license will do, but some agencies may insist on an international permit. They're free and easy to get from the relevant government agency in your home country.