A grinder is a necessary thing:
The other element most stores never mention is the grinder! All commercial espresso bars use one, because the grinder is critical to the espresso making process. Unlike drip coffee, espresso is a fussy process. To get an ideal espresso you need these things:
:: approx 14g of coffee ground fine enough to be extracted (have the shot 'pulled') yielding 1.5-2 ounces of espresso within 23-27 seconds

Why is this so critical?
True espresso machines are designed so when you follow these parameters, the machine will produce an espresso shot of a certain viscosity- and a shot with little bitterness or sourness, depending on the temperature of the brew water and the beans you used.