Alright, I am trying to setup my Peppermint OS linux up for two kinds of connections. eth0 with no internet (connecting to my ps3 to stream media.) and my wlan0 so I can still browse the internet while I am streaming media to said PS3 simultaneously. I have no idea how to do this. KNetwork Manger finds them, but it only lets one be active at a time.

I'm absolutely sure it is possible and a quick google tells me that people have done it and there is info on it using iptables and routes. For more info I'd try a networking forum (if such thing exists) or some such.

This should all be possible through the UI - i've done it previously.
I gather the eth0 connection simply refuses to connect?

If so, you may need to either place it in internet sharing mode, or assign a static IP on both the PS3 and your computer. Both methods are easy enough to do - and are possible through the UI.

This is a cool idea... I've checked my wicd client for KDE but find no reference to "internet sharing mode". Is there such a beast in knetworkmanager? If so I may consider switching over again after all these years.

It certainly is possible - although not immediately obvious. It isn't complicated to configure - just change a single drop down.

http://imagebin.org/161135