A straight forward method to solve Colebrook Equation in Excel or OpenOffice is presented in the book:
The following papers appeared in web describes various alternatives of Colebrook Equation and methods existing by Thomas G. Lester, P.E., Bergmann Associates
The author sugges VBA and UDFs as the methods by which Colebrook Equation be solved!
http://www.cheresources.com/colebrook1.shtml
http://www.cheresources.com/colebrook2.shtml
http://www.cheresources.com/colebrook3.shtml