more recent and complete guide http://news.nemcoin.com/nem-alpha-one-click-install-client-is-now-available/
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We know everyone is awaiting the one-click installer and I can assure you that it's coming very soon.
In the meantime we want to show you how it works.
First thing you have to do is browse to a website that will be disclosed when it's ready.
Probably looks something like this:
Once you click launch NCC the install process is started. Since everything is signed with a certificate you don't need to worry about checking checksums or anything. If it's signed with our certificate - it's from us (unless someone steals our certificate and hijacks the webserver but let's not assume that)
You will have to confirm that you want to run NCC:
After that The download will start:
(yeah double %…we know ;))
Once NCC ist started it will download NIS
and you'll have to confirm that you really want to run NIS:
Upon startup, you should see NCC landing page, where you can create or open wallet; PLEASE DON'T do it just yet. You should wait a while for NIS to be fully downloaded and launched. The easiest way right now is to check http://localhost:7890/chain/last-block in another tab. This is of course a thing that we'll make more convenient in the future - remember we're in alpha right now.
You can find in the NCC's menu a "Close
Program" tab which will shutdown NCC, but not NIS (so it will be harvesting in the background).
From this point on you'll never have to do this again. When there's an update it will be downloaded automatically.
PS: Yes it's more like 3 or 4 clicks and not 1 but only one is really from our software. The rest is Java wanting you confirmation. This aids your security though. If the certificate displayed looks fishy you know something's up and you shouldn't confirm the start of the application.