First off, having integrated components will always have an adverse effect on performance. However, with the availabilty of 1GHz and faster processors, most computers can handle intergrated audio with no noticable performance difference. Integrated video, for now, is always a bad idea when talking about a gaming system. The nForce, supposedly fixes that.
I may be a Doubting Thomas, but I won't trust the nForce until it comes out and can be more acurately tested. As for the SiS735, most of the motherboard manufacturers that use that chipset are not at all known for either stability or performance. Therefore, while the video might not hurt performance much, the performance is sub-par to begin with. Another issue with integrated video is that it shares your system memory. This means that if you have 128MB of system memory and you want to have a decent ammount of video memory (32MB or more), you will only be left with a maximum of 96MB of system memory. Not only that, but your system memory will always be slower than memory integrated onto a video card, and a GPU will always run faster than your chipset/cpu trying to do video along with everything else it has to worry about.
So... I would go with a motherboard that has an integrated Creative audio chip (none of that AC'97 crap). Integrated video on any platform available as of this moment will have a huge negative impact on gaming. A decent, cheap gaming video card is the GeForce2 MX400. It won't give you quite the performace of a GeForce2 GTS or Pro, but it will get the job done on almost any game available.
As for integrated NIC, a PCI network card can be found for as little as $15 so that isn't an issue at all.
I apologize for the length of this post, but I figured I would give you as much information as I have. All of the information here is correct to my knowledge. If someone wants to correct something I have said and substantiate it with fact, then go ahead. I am open to correction and constructive criticism.