Many times I find myself in the situation where I need to retrieve items
which need a more complex Caml query.
These procedures will give you a start

public static string CreateCAMLQuery(string[] parameters, string fieldName, string type)
       {
           StringBuilder sb = new StringBuilder();

           //if (parameters.Length == 0)
           // AppendEQ(sb, "all");

           for (int i = 0; i < parameters.Length; i++)
           {
               AppendEQ(sb, parameters[i], fieldName, type);
               if (i > 0)
               {
                   sb.Insert(0, "<And>");
                   sb.Append("</And>");
               }
           }
           sb.Insert(0, "<Where>");
           sb.Append("</Where>");
           return sb.ToString();
       }
       private static void AppendEQ(StringBuilder sb, string value, string fieldName, string type)
       {
           // put your field's internal name in place of Category   
           sb.Append("<Eq>");
           sb.Append(string.Format("<FieldRef Name='{0}'/>", fieldName));
           sb.AppendFormat(string.Format("<Value Type='{0}'>{1}</Value>", type, value));
           sb.Append("</Eq>");
       }

I hope it helps !!!