At the present time, it looks like the only app that will support video chat between a Tab and a PC is ooVoo. I have it on my Tab and have used it successfully for video chatting between it and 2 different laptops (one XP and one Vista Ultimate). It worked great in both situations. Obviously, the experience was better when the Tab was running on WiFi. It was still useable when the Tab was on 3G.
I have tried the Yahoo Messenger video plugin for the Tab but was never successful in getting the video working both ways (Tab-to-PC and PC-to-Tab). Posts I read in various forums indicated that this was a common experience.
Skype has made some noises that they will be releasing an Android app that will support video but so far, we've seen nothing. When you take into account the various issues that exist with Skype with some carriers (3G vs WiFi), I will be surprised if we ever see anything.
I’d like to recommend “Tango” which is the best video chatting app for iPhone, iPod touch and Android devices on 3G, 4G and Wi-Fi. You can video call your friends and family around the world.