Linux X.Org driver
This chip is supported by the 'neomagic' driver as part of the X.Org distribution. To get the XV extension (for accelerated video output, e.g. with mplayer) to work properly with videos above approx. 340x288 an entry like Option "OverlayMem" "1000000" in xorg.conf is required. Videos above dvd resolution produce garbled output, however.
Display on the internal LCD works as long as you set the monitor settings correct.
External VGA port
Only up to 1024x768 @ 24-bit, 1280x1024 @ 8-bit. This is despite the 4Mb video ram which should allow 1280x1024 @ 16-bit but low memory bandwidth limits this to 8-bit.
Composite video out
TV-out functionality is available under Windows 2000 with the driver supplied by IBM (v5.39). You need to delete the .inf supplied by Microsoft (neo20xx.inf) to force an install of the IBM driver as Win2k will otherwise prefer the Microsoft one. You will know that you're using the Microsoft driver if the NeoMagic tab is missing from your advanced display properties. It also refers to the adapter as a "MagicGraph256ZX" as opposed to the IBM driver which labels it "MagicMedia256ZX".
It is also available under Windows 9X series (95/98/98SE/ME) using the IBM drivers provided on their website. All TV out modes run larger than the TV screen, even at 640x480. Video out is supported only at 256 or 64K colors at 640x480 or 800x600 resolutions. Additionally, settings are not preserved on reboot.
This works the same as the Composite port, but you get a cleaner video signal when run over S-Video. Only some of the video out dongles available support S-Video output, and it is an option of the dongle, not the video drivers.
Linux kernel Framebuffer driver
With 2.6 kernels, the neofb driver seems to work pretty well. My rc.local (on fc3) does a modprobe neofb which automatically puts me in 1024x768-60 mode with 48 cols x 128 rows.
I do not use neofb for X...