Follow these steps and you'll have your AdMob Publisher ID in no time!
1. Go to AdMob.com and sign up.
2. Choose Add Site/App from the menu
3. Pick 'Android App'
4. Fill in the App Name, Category and App description. You don't need to enter the Android Package URL as you won't know it until you've put your app up in Google Play anyways. Leave that completely blank.
(Make sure you remove all text from the URL field if you don't use it, e.g. remove the default "market://" text.)
5. Click OK.
6. You'll then see a screen that talks about the AdMob Android SDK. This is the confusing part. Just ignore it and click the 'Go to Sites/Apps' button at the bottom. You don't need to download the SDK or anything. AppsVolcano takes care of that part for you already.
7. Now you'll see a list of your Apps. Find the app you just added and hover over the name with your mouse. You'll see a Manage Settings button appear. Click it.
8. That's it. You'll see your Publisher ID up at the top. It is below the App Name and below the Site URL. It is labelled 'Publisher ID' and is a 15 character code (alphanumeric).