unity won't start with nouveau driver on notebook with GeForce Go 6100 and more than 2G of RAM

I have an old notebook with an nVidia GeForce Go 6100 video controller. It works fine with Ubuntu 10.04 using the nv X video driver.

I've made a clean install of Ubuntu 12.04. It used the proprietary nVidia drivers and didn't work. I removed the nVidia drivers and tried the nouveau drivers. That didn't work. By using the kernel parameter "nomodeset", I forced the use of the VESA driver, and that works fine, but cannot use the native resolution of the display.

I've updated all packages to the current level, as of 2012 June 15. I'm trying the nouveau driver again.

1) lightdm appears to work correctly
2) unity just paints the background and nothing else seems to show up

dmesg and /var/log/Xorg.0.log have some suspicious entries:

in dmesg, lots of messages like this, and variants:
[drm] nouveau 0000:00:05.0: PFIFO_DMA_PUSHER - Ch 3 Get 0x01256038 Put 0x011c60b0 State 0x4ffe0004 (err: INVALID_MTHD) Push 0x00000000

In Xorg.0.log, this message:
[ 79.451] [mi] EQ overflowing. Additional events will be discarded until existing events are processed.
[ 79.451]
Backtrace:
[ 79.451] 0: /usr/bin/X (xorg_backtrace+0x26) [0x7f03a3c65866]
[ 79.451] 1: /usr/bin/X (mieqEnqueue+0x263) [0x7f03a3c45f43]
[ 79.451] 2: /usr/bin/X (0x7f03a3add000+0x62934) [0x7f03a3b3f934]
[ 79.451] 3: /usr/lib/xorg/modules/input/evdev_drv.so (0x7f039b6e2000+0x5d88) [0x7f039b6e7d88]
[ 79.451] 4: /usr/bin/X (0x7f03a3add000+0x8ae07) [0x7f03a3b67e07]
[ 79.451] 5: /usr/bin/X (0x7f03a3add000+0xb0d4a) [0x7f03a3b8dd4a]
[ 79.451] 6: /lib/x86_64-linux-gnu/libpthread.so.0 (0x7f03a2e03000+0xfcb0) [0x7f03a2e12cb0]
[ 79.452] 7: /lib/x86_64-linux-gnu/libc.so.6 (ioctl+0x7) [0x7f03a1d61d27]
[ 79.452] 8: /usr/lib/x86_64-linux-gnu/libdrm.so.2 (drmIoctl+0x28) [0x7f03a02f41a8]
[ 79.452] 9: /usr/lib/x86_64-linux-gnu/libdrm.so.2 (drmCommandWrite+0x1b) [0x7f03a02f649b]
[ 79.452] 10: /usr/lib/x86_64-linux-gnu/libdrm_nouveau.so.1 (0x7f039fca6000+0x2bd7) [0x7f039fca8bd7]
[ 79.452] 11: /usr/lib/x86_64-linux-gnu/libdrm_nouveau.so.1 (nouveau_bo_map_range+0x109) [0x7f039fca91f9]
[ 79.452] 12: /usr/lib/xorg/modules/drivers/nouveau_drv.so (0x7f039feac000+0xb15d) [0x7f039feb715d]
[ 79.452] 13: /usr/lib/xorg/modules/drivers/nouveau_drv.so (0x7f039feac000+0xb819) [0x7f039feb7819]
[ 79.452] 14: /usr/lib/xorg/modules/extensions/libdri2.so (DRI2SwapBuffers+0x110) [0x7f03a00ed790]
[ 79.452] 15: /usr/lib/xorg/modules/extensions/libdri2.so (0x7f03a00eb000+0x37d3) [0x7f03a00ee7d3]
[ 79.452] 16: /usr/bin/X (0x7f03a3add000+0x4e7a1) [0x7f03a3b2b7a1]
[ 79.452] 17: /usr/bin/X (0x7f03a3add000+0x3d6aa) [0x7f03a3b1a6aa]
[ 79.452] 18: /lib/x86_64-linux-gnu/libc.so.6 (__libc_start_main+0xed) [0x7f03a1c9876d]
[ 79.452] 19: /usr/bin/X (0x7f03a3add000+0x3d99d) [0x7f03a3b1a99d]
[ 79.452] [mi] These backtraces from mieqEnqueue may point to a culprit higher up the stack.
[ 79.452] [mi] mieq is *NOT* the cause. It is a victim.
[ 80.610] [mi] EQ overflow continuing. 100 events have been dropped.