Hi Mat,
No you can't do the Inca Trail independently, there are many restrictions on the trek now, and you need to get a permit (the company that you organize to do the trek through will arrange this for you), but be aware that permits sell out a fair way in advance - especially in May / June / July (high season).Unfortunatly, this is also the best time to go due to weather. But the coldest! The trail is closed in Feb every year for the whole month. Machu Picchu is still open in Feb though. There are 500 permits available for any given date, so 500 people can begin the trek each day - this includes porters, guides, cooks and trekkers...

Acclimatization?
If you are coming from La Paz, you shouldn't need to spend too much time in Cusco - you should already be acclimatized. If you are coming from Lima - definitely spend a few days in Cusco acclimatizing first or you will probably not enjoy your hike too much!!

Who can go?
If your Grandma is 55 and very fit, then you can take her, if not, I would say definitely not. It's not a stroll in the park!

Other options?
There are quite a few other options to avoid the crowds - Lares trek is the most popular. There is also Salkantay and choquequirao (this does not finish in Machu Picchu though) All of the other treks spend the final night in Aguas Calientes, usually in a hostal instead of camping (hot showers!!). Then take the bus or hike up the hill to Machu Picchu on the final morning. All the other treks still have stunning scenery, Lares offers a bit of a cultural experience as well with visits to a school and villages on the way through the mountain passes.

What do you need?
Most tour companies will provide you with most of the stuff you need for the trek, but in the long run, the old rule - you get what you pay for - definitely applies here! You will ofcourse need warm clothes, sleeping bag (or you can hire one), good hiking boots, and a new rule coming in now is that you need a non disposable water bottle - they are banning the old throw away water bottles totry and cut down on waste.

Where do you start?
Most tours will start in Cusco and transport will be arranged to get to the start of the trial from there. This should all be an inclusive package when you book the Inca Trail.

Hope that helps!! Kris