I doubt you'll be able to play Doom 3 on that SIS. I mean, 64mb of ram...my GeForce4 has 128.
You're right, but I don't see what the amount of memory has to do with it. Notebooks have shared memory anyways, don't they?
Also, if it's something with "Radeon" in its name, can I be sure it's a good accelerated card?
More or less... but, memory bandwidth is the primary factor in choosing onboard video. I usually go by what memtest86 tells me. Seems to be very accurate.
For example, an A7N8X-VM motherboard has about ~1.3GB/s at DDR333. That's awesome, because it has onboard video (GF4 MX440). It can play all sorts of games.
The K7VM2 I have here has ~360MB/s bandwidth (DDR266 though). It is pathetic. It simply cannot play games. It has trouble with 2D stuff The video chip on it is a VIA ProSavage 8.
Finally, a A7N266-VM gets ~640MB/s at DDR266. It's video is far better than the K7VM2, but is a little over half as good as the A7N8X-VM in benchmarks.
These are all desktop solutions, but I'm doubtful notebooks will be completely different. So, find out how much the memory can pump out. That's the most important factor.
Not to say the chip is completely irrelevant, but in terms of nVidia VS ATi for onboard solutions, that's fairly accurate.