Learning to read music does not require a 400 page tome but a short 'these are what the dots mean' explanation. THe difficulty (which is less so now) is finding source material to [i]practice[/i] reading. In my day, the books were full of Campdown Races, Franki and Johnny and excerpts from The Trout and had no value for me as a player then or now. Nowadasy there are more options (many transcriptions are on here).
FOr instance, learning what each note means is easy. Take a blank sheet of music paper and write a series of notes in straight crotchets, four beats to the bar (i.e. no rhythms to read). Write out 8 bars of two notes, say A and B in a randon sequence (ABBAABAABABBAABABABBABABAABAB, for instance) - concentrate on reading those two notes alone until you get the 8 bars right (if you find you have learned the sequence, write out another one - you are learning to read, not to play this sequence of notes). Then Write out eight bars using only A, B and C. THen try 16 bars of A, B, C & D. and so on. I recommend you don't learn those mnemonics (All Cows Eat Grass etc) because they tie you into a process that slows you down. Just learn two notes, then add a third then a fourth and so on. You will be reading sraight crotchets in no time. Then you can start looking at reading rhythms after you know what the notes are.