Which model AAO is it? The 110, the 250?
I have an Acer Aspire One D250 with Intel GMA950 and 1GB RAM, running Windows XP (factory default), and Sacrifice runs like a dream. I even edited the registry to make it run widescreen, and at the default netbook resolution (1024 x 600) it suffers from none of the problems noted at the WSGF (i.e. no disappearing objects, as far as I can tell).
Vista is notoriously problematic and quite a resource hog in and of itself, so I am quite surprised it even runs on a netbook. To the best of my knowledge, Acer doesn't release any netbooks running Vista for exactly that reason, and if you're running an illegal version of Vista (not saying that you do, of course), that might be a problem too. My first solution would be to switch back to Windows XP or, if you are unwilling or unable to go back, I would upgrade to Windows 7 and see if that works. While the latter is a slimmed-down version of Vista, it is somewhat better.
Edit: changed a word.

Could you please tell me the hexcode for the 1024x600 resolution?
I can't get it right ._.

There are converting tools online, e.g.:
http://easycalculation.com/decimal-converter.php
The code for 1024 is "00 04 00" (400) and for 600 is "00 02 58" (258), so you would have to change the registry key to read:
00 04 00 00 02 58
Some people report that objects disappear at certain angles. I don't think this has anything to do with widescreen, but rather with very high resolutions (1920x1080, etc.). I haven't spotted any errors on my Netbook playing at 1024x600.
More information at WSG forum:
http://www.widescreengamingforum.com/forum/viewtopic.php?f=56&t=11566&start=0
Let me know if this worked for you.

Works like a charm
Thank you very much

agh i WAS running a legal version of vista but now that netbook has gone to hell! anyway i bought a new laptop JUST for this game haha.....and it works awesomely :D