I have not used USART interrupts myself yet, but these might get you started.
http://darreltaylor.com/DT_INTS-18/
http://www.microengineeringlabs.com/...bp/serbufx.bas
http://www.melabs.com/resources/samples/pbp/usart.bas
http://www.picbasic.co.uk/forum/show...rial+interrupt