I just want to pass the hoover dam so Im on the east side of the river where the legion fort is.

is the only way through the 'innacessable' gate via the MQ?

Erm, you can't get to the east side of Hoover Dam unless you do the main quest. (Final quest, point of no return.)
But if you mean "The Fort", you'll have to go there by boat down at Cottonwood Cove. (Or fast-travel after the first visit.)

yes, I'm pretty sure. you can't use it as an access point from the legion to the NCR side, if that's what you meant.

damn. beat me by a minute. your probably more helpful than Bethesda's half-assed customer support, gabriel.

well I havent even touched the main quest yet but wanted to goto legion territory as part of my RP... so theres no way across unless i do MQ?

yup. unfortunately. theres nothing over there anyway. just "things" that can only be accessed during the MQ.

You can swim across the Colorado to the South of the dam. I haven't tried it yet myself, but have heard it can be quite tough on that side of the river.

There is no way across the Dam, but you do not need to be on the MQ to get to the Fort. You just have to pass a skill challenge. However the early part of the MQ, before you pick a side, gives you an invitation to go to the Fort.

However go to Cottonwood Cove and just take the boat up to the Fort. As long as the Legion does not Hate you or worse, you can go there anytime you want to.

You need to finish Ring-A-Ding in order to gain access to the Fort, since the raft will not function until you get the Mark of Caesar after either dealing with Benny or letting him run off. Cottonwood Cove, on the other hand, can be gone to at any time, however if you are hated by the Legion you'll start a massive fight by doing so.

Even though Ring A Ding is Act 1 of the MQ, I don't really consider it the MQ. Just an introduction to all the major players in the game.

Well you can get there as early in the game as you like without doing any quests if you want to take advantage of a glitch:

http://fallout.wikia.com/wiki/Legate%27s_Camp#Notes

I haven't tried this since the last patch though so don't know if they sealed that particular hole in the wall. Try it! It's fun!