I cannot say I ever bother about achievements but this was an interesting question.
Achievements on Steam CAN be reset, Team Fortress has/used to have(?) support for this via the built in console, not a game I play. The ability to reset Achievements may depend on how they have been implemented, I have no idea of the ins and outs.
A third party application, Steam Achievement Manager, allows you to reset Achievements in some games. It DOES NOT currently support NV.
Now for the warnings:
Before attempting to reset Steam Achievements you should first contact both Steam and Ob or Beth. If they say no, and they probably will, I'd think twice about trying. The reason for contacting these companies is to avoid as best you can any chance of having your Steam account locked through suspected hacking activities. Contacting them may also highlight this feature as one they could implement at some time in the future.
I would certainly think twice about running ANY software not officially sanctioned by Steam that connects to my Steam account.
I also thought twice about posting this information as it may prove dangerous but it took less than ten seconds to search out the basics so I think the warnings justify the post.
Hi ecat,
Thank you very much for your reply and information. Very much appreciated :tops:
This is the Only game I have using Steam. To be honest I had never heard of it before this game. :blush:
Having explained briefly reasons for a clean install. Just started a New Game, issues have come up which wouldn't happen with a clean install. but I could be wrong."Not the first time" lol
Come out of the Doctors,"LeveL 1". walking around the town as you do. First creature I come across is A Giant Radscorpian.

oo:. One of the persons for the first Quest had already been killed. Far too powerful Creature for a Level 1 Players. Good Job I knew where Victor was lol

A little bit further on, go into a house.Only just managed to get in. Why you might ask. Theres 2 Longhorns eating the frontroom Carpet.lol :rofl:
When reinstalling its not coming from the Disk, but its downloading over the top of the game it has not clear beforhand, causing overlapping.
Maybe i'm being dumb, whats the point of having the game on Disk if Steam ignores it.Seems like a waste of a Disk. :shrug:
Thats my moan for the day.lol
Thanks again for your reply,
James.