The max res for one screens-worth of video from a 4200, video out, is 800x600. After that, it does a pan-with-your-pointer thing, where it shows as much of the screeen as it can, and follows your mouse around after that.
However, television resolution is less that 800x600... if you have a professional monitor, you might be able to see like 720x486 or so pixels, but most televisions only display 640x480. Beyond that, and you need a decent scan converter if you want to be able to read the text on the screen (alot of cheap scan converters just shrink the picture, which doesn't work so well for text... a good SC has more image processing that goes on to fix these sorts of problems).