Yes you can, but you need an adapter to do it correctly. Here is a place to go: http://www.tvandnav2go.com
It does only the video. And yes, you can do the audio too, but most likely you'll be disappointed. I say this, because the stereo produces EVERYTHING, and one thing you don't need it the high frequency noise we all have to put up with. I have an article on my web site about this; Audio Filtering.
The TVandNAV2go unit is half the price ($240) of the competition, and works just as well as the highest priced one ($495). However, the manual is junk. If you end up buying one for your Toyota, and you cannot get it to work, e-mail me and I'll tell you what needs to be done. My address is in my profile, and on my web page as well.
By the way, you cannot hook into the navi directly. The Icom video output is NTSC, and the navi requires RGB, with sinc on green or horizontal refresh as the case maybe.