giving output bits of counter to logical gates in system generator
You could use a block called bitbasher. It's a block with which you can individually manipulate the bits on a line. If you open it you should be able to write some code. Just write something like: $$b = \{a[1]\}$$ $$c=\{a[2]\}$$ $$d=\{a[3]\}$$
It'll create 3 outputs (b,c and d) and 1 input (a). 
The number within the brackets mean the number of the bit of the line you want to use.

For further reading I suggest: http://www.xilinx.com/support/sw_manuals/sysgen_ref.pdf.

When I was learning how to use system generator, it helped a lot.