Done it for the last two summers on a hardtail, its good fun. You'll only really suffer on the main Les Gets track cos of all the braking bumps (all the way down)
Pleney is ok apart from the berms out in the open which are always very rough
I found stopping for a couple of minutes half way down sorts you out.
Im not a great rider but theres some unbelievable shite riders out there, you wont be slowest down the hill (unless your unbelievably shite)
Just make sure you have some dual ply tires, some decent forks (the bigger the better really) and some good brakes
I used some 66 RC2X's the first time on my hardtail, and they were great.
I used Z1's last year and they felt a bit weedy.