Yes, you can do fring/skype video chat with someone on a computer.
with fring it's really simple. add skype. click on your contacts name. 3 icons come up, one with a message button, one with a phone button, one with a video camera. press the video camera, and wait for the other person to accept. and there ya go! you're video chatting. took me a second to figure it out myself.
1) In Fring, when you're on the main screen (the screen displaying the list of contacts), tap the MENU button and select ADD-ONS.
2) Select SKYPE.
3) Input your Skype username and password.
4) On the main screen, select your nephew's username.
5) Select the VIDEO CAMERA icon (this will call your nephew)
6) Nephew answers the call and the camera automatically turns on.
Skype to Skype calls are free. You only get charged when using Skype to call landlines or cellphones. So using Fring on your Evo to call a person on Skype is free.
Sorry, I don't use any other type of IM client that does video calls, so I wouldn't know the answer to your second question.