First, ignore the ME, CE PPC prefix as this all means the same.
CE2003 = ME2003=PPC2003. If the driver says it is for 2003SE, you are OK. Ik not. just try installing the 2003 driver and try it.
Unfortunately, my research shows that the internet is littered with driver problems as this keyboard is generic, unbranded and so their is no site to download a driver from... Loose the CD and you have a problem.
What I have found is that the IR503 is manufactured by
http://www.citipack.com.tw/
They have a web site, BUT, the IR503 is not listed, they list only the IR501 and IR502.
