I've been a Windows and Ubuntu user for years and, as such, have a Dell UltraSharp 27" (with HDI). I will be buying a 27" iMac. Will I be able to plug in my Dell screen to my iMac and have a split display? (I believe that I can, using a specific cable.) What will the screens look like? Will the dock be on both screens? For example, will I be able to have Photoshop open on the iMac, and mail open on the Dell?