Well i've got to new vegas and benny isn't there, you're supposed to chase him to a fort at the other side of the hoover dam. But theres a problem, one big motha of a problem...

There is absolutely no physical way onto that island.

There are unscalable cliff faces on all sides, there are a couple of lakelurk cave areas (not very big). There are also gentle slopes that have magic blocking walls on them (seriously this is stupid we're not in the 90s!) But i have been around the island completely and there is no way onto it. Incredibly, no one else has discovered this yet as i did a forum search and no one has written about this problem yet. I spent two hours going round (with god mode on as deathclaws are unbeatable in this game) and there is no way up. I know how to use noclip mode but no instruction has been given that this must be done to get onto the island, in the game.

Have i broken the game in a special way or something?

You don't just walk onto the island.. you have to go a bit south and you take a boat there. If you would actually read dialogue and quests you would know that.

There has been no indication in any dialogue that i needed to get a boat to the island, further more there is no NOTE in my inventory, and no marker leading to a boat on the map. The map only says to go from new vegas to the fort.

Make sure you have this specific quest selected or the way points won't show up. It's actually not a "little bit" but almost all the way to the southern most part of the river you take a ferry from one of Caesars goons. It works like a door on a house, activating him and the raft accesses that area.

If I had the game on this computer I could pinpoint the exact square coordinates for you... but it's lower part of the river west side of the river. You can swim south in the river but beware... there are a bit of LakeLurks in that river in a cave that will follow you all the way there (personal experience).

Good Luck