Where do I get a SIS mirage 672 vga driver?

Even though the package xserver-xorg-video-sis contains most of the SiS drivers for Xorg and will be installed automatically when you install Ubuntu, it does not yet contain proper video drivers for one or two particular SiS chipsets such as 661 and 671/2, although you might get acceptable resolutions with the fallback driver.

There is quite a detailed discussion on Launchpad about the issue and that contains links to resources that detail how to compile and install the drivers. It can take a bit of time to set up the drivers, but that Launchpad page contains the most up to date information on the current situation. There is also some very useful information and a compiled driver on this webpage from one of the active Launchpad contributors on this thread.

There is no 3d hardware acceleration (DRI) for SiS chipsets in general (apart from the very old 300 series, and even that will be very poor because of the age of the chipsets).

I discuss the SiS M650, 670 and related series of integrated GPUs in the questions below, and note that there is no 3d hardware acceleration available, but the limited video hardware acceleration (e.g. for DVD) and 2d acceleration should be usable:

• How to enable 3D acceleration with Sis Vga 771/671 on Ubuntu 12.04
• https://askubuntu.com/questions/179365/resolution-problem-on-12-04-sis

See my answer here relating to the problems affecting 650, 660, and 670 SiS chipsets on 12.10, which should be fixed by the time Raring Ringtail (13.04) comes out:

• How to troubleshoot a “Low Graphics Mode” installer error on PC with SiS iGPU?