My dad is riding in the 100 miles for diabetes ride thingo in january, and mum is freakin' out because she thinks he will have a heart attack. He's 44 or so by the way, if you've ever done 100 miles then posting up a training schedule, diet and whatever other tips would be great. Thanks.
This one is easy....
Go here:
http://www.ultracycling.com/
read, and then ride your bike lots.
also look up a book by Ed Burke and Ed Pavelka "The complete book of Long Distance Cycling" (ISBN: 1579541992 ) which includes training schedules, diet tips etc... and some of the issues you will expect
I don't know the route, but generally I'd say 160km's on road is a doddle, especially if you're with a group that's plugging along at a reasonable pace that you're comforable with. And that's the sum of it, plod along at a reasonable pace that leaves you not puffing, eat early, eat often (no big feeds but continuous stream of stuff ) And most people of reasonable fitness can ride 160km's on road.
For training, As a *very* rough basis plot over 12 weeks whatever the longest distance your comfortable with now, and increase that bit by bit up to 75% of the distance two weeks before, cut 50% the week before then go from there. that should be your long ride in the week, with whatever smaller rides you can get in through the rest of the week.
You're less likely to have a heart attack over long distance as long as you keep your food and water up 'cause you're not pushing that hard. If you are, you're probably not going to last the distance. (but I'm not a doctor so meh
I've broken the 100miles about 5 or 6 times on dirt this year and a couple of times on the road just by plodding along, and keeping the food and hydration flowing... and hopefully again once more this weekend

the times I've struggled are when I've either just had a bad day or have gone hard early in the ride or forgotten to eat enough.
HTH
Cheers
Gonz