The Elves and Dwarves update to Guardians of Graxia is to be released on the 1st February 2011, it was announced by Berek over at Petroglyph here.
The new expansion will consist of Elves and Dwarves (I reckon that you already guessed that part), Flist the deceitful Elf and Broxin the greedy Dwarf are two new Guardians that will feature in the expansion along with 14 new units to battle with on six brand new maps.
It was also announced that a demo will be released on the day of release, which again is February 1st so you can try out the new expansion before you buy!