How do I in-system program LPC17XX?
You can use the lpc21isp programmer which was originally written for the LPC21xx series but  recent versions also support the LPC17xx series. It requires only a serial port but it is helpful to connect the RESET and ISP pins because they will have to be manipulated to force the chip into the bootloader.

There are binaries for Windows and the code compiles without problems on both Linux and OS X.

PS. There is also JTAG but who would want to use that. :)