Are you looking at our own Galaxy or at other Galaxies?

First of all, there are many SETI programs ongoing, not just one. Some look
at all-sky surveys, some at particular stars. The all-sky-suveys (like
seti@home) certainly touch on (have the antenna pointed at) other Galaxies
at least for some time fragments, but there is no specific program (that I
know of) that focuses on extra-galactic signal detection.

A simple question, if there was an intelligent signal coming from a
distant planet how on earth could we get it out from all the noise?

That's the job of RFI filtering. It is noisy out there, so there are some
very strict rules with which a signal has to comply to be even considered at
extra-terrestrial. For example, it needs to repeat itself, at the same point
in the sky. Check out this site, and some of the other news letters from
seti@home :
http://setiathome.ssl.berkeley.edu/newsletters/newsletter6.html

You only have one receiver I am guessing or do you have multiple
receivers like a beamformer?

Again, there are many SETI programs on-going around the world. An overview
of them is regularly posted on this news group and on sci.astro.seti.
seti@home analyses signals which were received by piggy-backing on the
Arecibo receiver.
Beamforming, by phase-synchronizing multiple receivers will greatly increase
resolution of a receiver, but not its sensitivity. Since SETI searches in
general are more interested in finding ANY signal than to find out exactly
where it comes from, linking-up multiple receivers across the world has not
been a great priority. It might make RFI filtering easier, but then the next
problem comes in play : most SETI programs are heavily underfunded, and have
no control over pointing a radio telescope one direction or another. Let
alone having two telescopes phase-synchronized pointing at the same point in
the sky.....

The Allan Telescope Array (ATA) project will change all this, when hundreds
of small telescopes will be phase-linked to form a big, very programmable,
phased array, which will be able to look at many points in the sky
simultaniously. And it is mainly dedicated to SETI. Do a Google search on
this. It's quite an amazing project.

What SNRs are you dealing with (can you
cope with).

I believe that an 8db SNR ratio is required for seti@home. Much lower and
there will be way too many false-negatives.

Has it ever been tested from space ie could voyager or
equivalent give out a signal (at random) and see if the system works?

seti@home still detects the Pioneer 10 signal.... It works allright !

Thanks

You are welcome.
Please read the seti FAQ pages. They contain an amazing amount of
interesting facts :
http://www.setifaq.org