Ok, I just looked up the trip, and it's not an actual accent of Mont Blanc, but the best parts of the Tour du Mont Blanc. Having walked a lot of the TDMB, I would say that it is not that hard. The trails are all very well marked and any tricky parts are equipped with ladders and handrails. The route takes in some of the most fantastic viewpoints in the Alps, so make sure to take plenty of photos!!! Altitude is very unlikely to be a problem, the highest point on the trail being 2665m. be sure to look out for the local wildlife, there are ibex, chamois, marmot, alpine chough and an abundance of wild flowers. Be sure to cover yourself with suncream, even when it doesn't feal that warm, the sun is very strong in July and that altitude inhances that. Don't forget lips, under chin and inside your nostrils!!!!

And make sure to have a Vin Chaud and slice of berry tart at the Lac Blanc Chalet!!!

Hope I'm not too late, you should be heading off pretty soon.

Technically there are several routes up Mt Blanc that are not hard- what mountaineers call snow plods, the difficulties are objective danger- in the summer that's rock fall and serac fall, and that's minimised by not being in certain places as certain times of day- your guide will see to that and the problem of altitude.

Hopefully your trip will include some acclimatisation- one of the easiest things you can do whether its included in the trip or you can tag it on before it take a cable car to the top of the Aiguille De Midi early in the morning, pack a picnic, a book, sun cream and camera and spend the whole day up there enjoying the view and chilling out working on the high altitude sun tan and growing yourself some more red blood cells- the steps in the telepherique station will take it out of you at first and you learn to pace yourself. You can also watch the climbers heading out of the ice tunnel down to the glacier and watch climbers finish routes at the station. 

Then some easy peaks- presumably they'll be taking you on a glacier to learn some rope work and up the Aiguille de Tour or similar to get you used to it, that's all good stuff. Unfortunately there's no way of knowing how the altitude will affect you, its only got me when I've worn myself out so plenty of rest (the outdoor pool in Cham is legendary- but take you speedos, no shorts allowed) and being as fit as you can be never hurts, so run up some hills at home first.

Enjoy and good luck, the mountain dominates the valley but never looks the same once you've conquered it, almost like you've wiped a smug grin of its face and brought it down a peg.