Linux, USB printer

I have a box running Red Hat Linux (kernel 2.4.20) and a USB printer connected to the box. My application has to throw a file to the printer. And here goes the question as I know pretty nothing about interracting with devices under Linux. How can my app know when the printer is connected or disconnected and on what device it is mapped by the kernel (/dev/usb/lp%d)?
Thank you!