It is, but, beware...
This adds the stream address as an entry to your library. This could cause it to crop up, for example, in a smartlist that generates a list of random audio entries from your library. That kind of thing. It's treated as just another audio track. I have quite a few saved in my library.
The trick is to tag them. I used a field called "Type" and set the streams as "Online Radio".
I then edited the "files to show" of the main audio branch to exclude all files of "[Type]="Online Radio""
Lastly, I created a new view under audio, that ignores the parent search rules, while itself, it's set to only include files of "[Type]="Online Radio"". This view is where I go to when I want a radio station of some sort to listen to. One of the bonuses of having them in the library like this is that you can also asign an image to them (Cover art) and tag them with genre, description etc. Just about all the ones I have saved also pause... and when you play, it resumes from where you paused... how neat is that?
I understand you've not been using MC for long, so hope that makes sense to you. I'm 'speed posting' as I'm about out of time here. Normally, I would take the time to expand upon that with pictures etc.. If you need that, just shout and either myself or someone else will explain further.
-marko