I am still learning LPC2148 hence can't give you code.
Process is.
make trig pin high
then a delay of 10 us
then make trig pin low
clear 16 bit timer
wait till echo pin goes high
when echo pin goes high start timer
wait till echo pin goes low
when echo pin goes low stop timer
use timer value and do the calculation to get distance
additional:
if timer overflows before echo goes low then increment a counter.
if counter is 1 add 65535 to timer value before calculating distance
if counter is 2 add 65535 * 2 to timer value before calculating the distance.
additionally use US-020 module which can measure 700 cms.