We can determine this from two terminals on G4 Sunbathing

... sending a light-speed transmission to Sol may be futile, but it is the only possible way to warn Earth
of a hostile alien race.

<G4 Sunbathing (Terminal 1)>

and later

The message will arrive in ninety-two years.

<G4 Sunbathing (Terminal 2: 'Success' message)>

One instant you're looking forward to retiring from combat as the
hero of the defense of Tau Ceti and the next you're on an alien world
seventeen years later and half a million light years away.

<Waterloo Waterpark (Terminal 1: 2nd message)>

For seventeen years the renegade Pfhor scoutship
jumped between the closely packed stars of the
galactic core: charting and discarding nearly
seven thousand systems before finally falling into a
slow orbit around the second planet of a dim star
ninety-seven light years from the gravitional
center of the milky way.

(Final Screen)

Based on these figures Matthew T. Russotto <russotto@pond.com> writes:

The basic problem here is that Earth isn't anywhere near 500,000 light years from the center of the Milky Way. It's about 8 kiloparsecs, or 26,000 light years, from the center of the Milky Way.

The Milky Way is only something like 120,000 light-years in diameter. 500,000 light years is even beyond the Magellenic Clouds (170,000 light years), though it is not as far as M31 in Andromeda (2.2 million light-years). Anything 500k light-years from a point in the Milky Way is in intergalactic space.

David Menendez <dmm264@psu.edu> while agreeing that a distance of half a million light years would leave the Earth in inter-galactic space suggests that Durandal was being hyperbolic for dramatic effect, much like people will say there were 'hundreds' of people there, when there may only have been a few dozen.

mmmmmmhhhh... I wonder if Bungie are listening?

Well the last time this page was updated was Nov 10, 1995 but it should have been updated with the following items from the What's New section. Thanks to Nathan Bitner <nathan@bungie.com> for drawing my attention to this.

Back in Nov 24, 1995 the What's New section has this to say regarding the Milky Way distance problem (above) in the Marathon 2 Preview and Demo.

Marathon 2: Durandal is out. One quick observation regarding the story so far is that Bungie has fixed the distance problem. Lh'owon is now only "thousands of light-years from Tau Ceti or Earth".

Yes Bungie did listen! :-)

Back in Feb 10 1996 the Tau Ceti to Earth distance problem was spotted. The What's New section had this to say on the subject:

Planning a trip to Tau Ceti ? So just how far away is it? 92 light years or 11.77 light years?

Concerning this problem Nathan writes:

If we've learned anything over the years, it's that you can't trust the damn computers.

Bungie knows where Tau Ceti is. It is the 24th closest star to Sol, at approximately 11.5 light years from Earth. The real question is, what were the AIs thinking?