it depends what tricks the newer Uefi-Bios has now.
You have to adjust Uefi-Bios for Ubuntu-allowed installation to efi-mode
resp. to legacy-mode.
It is explained here:
The acer S3 is not an absolutely brandy-hot-new model, so you should have luck with this link. But probably it does not work to install both windows and ubuntu together onto the partition where only 20 GB SDD is located. To get the maximum of it, I would install Ubuntu completely onto that notebook and try to use Windows 8 in virtualbox of Ubuntu. You can get virtualbox at http://virtualbox.org -
when you are clever: send back acer S3 to acer technical support and express your wish to want windows 7 instead of windows 8 - then you would have less problems with virtualbox and windows 7. But I dont know if you would get installation-DVD for Windows 7 from acer. In the end you could demand, that they delete Windows 8 and you get some money back and have then acer S3 completely free for Ubuntu ...