Hey I just got a Medion 5000 Station
I wondered how is the best way to connect an external monitor which would show me only the video when I am editing with Premiere Pro or Vegas but not the entire desktop and other stuff
You're probably going to need a regular tv with rca and/or super vhs inputs. You also need a video card with a breakout box. Hook the tv to the out terminals of the breakout box. That's how I do it with my Pinnacle DV500 card. Vegas Video has a diagram of another way to do this but it requires a video camera or monitor with a pass through feature. If you can support two monitors off your graphics card, you shouldn't be too unhappy.
Some cards, like the Matrox RT.X100 include realtime full-screen analog video output simultaneous with playback of the Premiere timeline. I have a television monitor hooked up to mine, just for the purpose of previewing the video.