We also took the Palace on Wheels in conjunction with a National Geographic tour, and thoroughly enjoyed it. Do not expect modern mod cons, though it is indeed "luxurious" in an Indian standard, and reminds one of the very old fashioned trains of yore, with lots of colour, even pomp. Your "Khidmatgar" and his assistant are at your beck and call in your coach, dinners are sumptuous (breakfast is put together at the end of your coach by your khidmatgar and can be quite basic and variable and the khidmatgars are very, er, practiced and rigirous at getting your tip - perhaps the only and minor flies in the very nice ointment,) and the excursions are memorable.

I'd highly recommend the entire trip of seven days' duration, and I'd add a week for other touring (e.g. Delhi / New Delhi and area, etc.)

The official Palace on Wheels website is pretty descriptive and useful.