i want to use uart in lpc2148.
U0RBR--> can be used for reading and
U0THR--> for writing ...

to use these registers is it enough to make the Divisor Latch Access Bit
(DLAB) in U0LCR zero

what all control or status bits should i use for effective use of uart?

Check out Martin Thomas' example projects for the LPC2138 (it's the same
as the LPC2148 but without the USB controller):
http://www.siwawi.arubi.uni-kl.de/avr_projects/arm_projects/