hi
yes it sounds like you will need drivers. The general rule is that one Arduino pin can drive one LED. For multiple LED's driven from the same pin or signal you need a driver circuit.
If I understand you correctly, you want different levels for numerous groups of LED's: instead of a group of LED's going on/off, you want them to be able to be able to put out a range of light levels from dark to bright.
So....if you have more than 3 batches (for the existing PWM outs), you'll need some kind of analog expander chip.
You can't fake the PWM expander as you have been trying to do above.. it won't work. You'll need something that multiplexes one output into many.
They are talking about just that problem here: http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1173831471
D