Verifying if a car is a sports car based on speed and horse power
_maxSpeed and _horsePower should be private.

You have (confusingly named) setter methods for public variables, but no getters.  That makes for an odd interface.

In C# you by convention use properties for getters and setters.  So instead of

public int _maxSpeed = 0;
public int _horsepower = 0;
public void maxSpeed(int newmaxSpeed)
{
    _maxSpeed = newmaxSpeed;
}
public void horsepower(int newhorsepower)
{
    _horsepower = newhorsepower;
}


You have

public int MaxSpeed { get; set; }
public int HorsePower { get; set; } 


Since these values are unlikely to change, you could make the type immutable:

class Car
{
    public readonly int MaxSpeed;
    public readonly int HorsePower;

    public Car( int maxSpeed, int horsePower )
    {
        MaxSpeed = maxSpeed;
        HorsePower = horsePower;
    }
}


Instead of checking a boolean expression and then returning a literal true or false, just return the expression instead.  Booleans are a type just like any other.  Also, you don't need the comparison to true or false for the same reason.

if( someCondition == true )
    return true;
else
    return false;


You have

if( someCondition )
    return true;
else
    return false;


or better yet

return someCondition;


So

return _maxSpeed &gt;= _MinimumRequiredSpeed &amp;&amp; 
       _horsepower &gt;= _MinimumRequiredHorsepower;


Whenever you take user input you need to check it.  Your program will crash if the user enters something that is not a number.  You can check this by using TryParse instead of Parse.

int horsePower;
do
{
    string input = Console.ReadLine();
}
while( !int.TryParse( input, out horsePower ) );


Other than that it is fine, keep at it ;)