The visa process for India is a bit of a pain in terms of having to queue at the High Commission (if you still have this option, it is the quickest way), but not complicated. You need to be invited by an Indian resident, so it may be that your husband will have to get out there first and get a letter of invitation for you, but this should be straight forward.
The cost isn't too bad, though they charge extra for US nationals, which I find bewildering, and I think comes from the days of the Cold War, when Pakistan supported the US so India took the opposite side for the hell of it.
I know it is horrible being apart from your husband, but really you could look on this as a wonderful opportunity to travel to an amazing country.
Re: vaccinations. This might help
http://www.netdoctor.co.uk/travel/asia/india.shtml My experience of vaccinations is 10 years out of date, but I know I had a tetanus and polio booster, typhoid, hep A and diptheria, and I think I had yellow fever, but I was out there for two years and it may not be necessary for a quick visit. I didn't take malaria tablets, but you should talk to your local travel clinic.
Where abouts will he be going?
Vicky