Skype compatibility issues

I am an old retired guy with no tech savvy at all. I ask these questions because I would like an expert opinion. I use a Dell Studio XPS PC and IE9 and I use Vonage for my phone service. I am thinking of getting Skype for its ability to send both sound and video. Questions: ( 1) Are there compatibility issues with Skype and Win 7? (I use Win 7). ( 2) Will Skype interfere with Vonage or vice-versa? ( 3) Is there a better alternative to Skype for sending video and voice that I have overlooked? (4.) When I upgraded from Vista to Win 7 there was a slight incompatibility with the old graphics card (sometimes when I move the cursor to the edge of the screen it goes black--move it toward the center screen and it goes back to normal. No big deal. Will this small problem interfere with the operation of Skype? Any help appreciated. Thanks. Greg