Problem initializing 4-bit mode LCD(DEM 20486 SBH-PW-N)
Assuming it's Hitachi HD44780-compatible you need to study the data sheet very carefully and follow it to the letter and it will work. There should be plenty of stuff on the net for an AVR if you want to copy, but I think it's best to figure it out (tm). 

Also, make sure you've got the contrast voltage input set to a reasonable value (near ground for normal temperature range units). The datasheet you linked is a bit confusing as it shows 4.5V for Vo. Note that voltage is relative to Vdd, so for a 5V supply it should be about 0.5V with respect to ground.