Elder Giant Magic (Secrets of Xen'drik p.135) requires a Concentration check each round you use it, and “You cannot take 10 on these checks.”
Steady Concentration (Races of Stone p.144) says that “You can always take 10 on Concentration checks, even when conditions would not normally allow you to do so.”
Assuming that you have both feats, can you take 10 on the Concentration checks to use Elder Giant Magic?