ALTERA DE2 and 1-wire sensor

It is much more easier.

Get in contact with Maxim, the companie that bought Dallas.

Ask for the 1-Wire Master source code available in verilog HDL

http://www.maxim-ic.com/appnotes.cfm/an_pk/119 (http://www.maxim-ic.com/appnotes.cfm/an_pk/119)

all you need is to write an avalon wrapper around that modul to interface it to nios II

and of course some software that controls this ip ...