[all variants] Reset APT, get rid of obsolete packages, help I'm stuck!

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http://ubuntuforums.org – I'm running Lubuntu 12.10 liveCD, persistent install on FAT32-formatted 4GB pendrive (3.2GB casper file - Unetbootin method). I can install packages, that's cool. I tried to install alternative kernel but it failed. Now I have linux-image-3.4.9-rt17-avl2-pae package as 'obsolete'. It's not... (Hardware)