well, then do this
ls -l ubuntu-11.10-preinstalled-desktop-armel+omap.img

if you get 'No such file or directory', then decompress it first


And the command sudo fdisk -l -u is informative, that should give something similar to
sudo fdisk -l -u meego-core-armv7hl-n900-1.2.90.0.0.20110824.2-mmcblk0p.raw

meego-core-armv7hl-n900-1.2.90.0.0.20110824.2-mmcblk0p.raw1 1 3583999 1791999+ 83 Linux
Partition 1 has different physical/logical endings:
phys=(1023, 3, 32) logical=(27999, 3, 32)
meego-core-armv7hl-n900-1.2.90.0.0.20110824.2-mmcblk0p.raw2 3584000 3600383 8192 82 Linux swap / Solaris
Partition 2 has different physical/logical beginnings (non-Linux?):
phys=(1023, 3, 32) logical=(28000, 0, 1)
Partition 2 has different physical/logical endings:
phys=(1023, 3, 32) logical=(28127, 3, 32)
meego-core-armv7hl-n900-1.2.90.0.0.20110824.2-mmcblk0p.raw3 3600384 3665919 32768 c W95 FAT32 (LBA)
Partition 3 has different physical/logical beginnings (non-Linux?):
phys=(1023, 3, 32) logical=(28128, 0, 1)
Partition 3 has different physical/logical endings:
phys=(1023, 3, 32) logical=(28639, 3, 32)

If you have such an info, then you 1)shure that it is what you need, that the image is decompressed and has valid partition table 2) can correct, if necessary, offset for mounted partition and check the file system type (it the offset is correct - you multiply sectors by 512, some tutorials claim, that it works when the number of sectors taken 1 less than in the output of fdisk, one can try probing 'close numbers of sectors' (but multiplied by the same 512) - then, having loaded modules for that fs, it should be mountable with that same 'mount')

(the exaple up I give is not probably the best, as contains some errors or 'inconsistencies', still that MeeGo was installable; but it gives the partition table info, that is what you need to know from your image in order to mount then it with correct parameters. I guess that in your case offset is correct but by some reason your quite up to date host OS does not understand fs of the image - maybe indeed, the file does not exist )