The recommended way to video chat between Mac and Windows currently is to use Skype. AIM does not support high resolution video to iChat even if your camera does and - as posted already - there are known issues when connecting between AIM and iChat. Yes, it can work with specific/compatible versions but, it is not recommended. Skype allows for higher resolution video using the built in camera and up to HD video using external cameras, it is cross compatible between Windows, Linux and Mac and has a better audio codec; so better audio fidelity. Skype is free just like AIM or iChat and will almost always provide better quality at the same bandwidth than AIM to iChat will.
There are tons of other 3rd party solutions such as Vid from Logitech, Meebo, Oovoo, etc, etc so try out a few and see what works best for you. To be blunt though, there are alot of sites out there that have already done extensive testing between video clients like these and none (of the free clients) have rated higher than Skype so far. Just FYI