Hmm... I'm not sure if you will be able to control IR-controlled curtains with an X-10 remote via IR543.

(Anyone, please correct me if I'm wrong, because I don't have an IR543.)

The IR543 receives IR signals and converts them to X-10 signals. It cannot do the reverse (i.e. receive X-10 signals and convert them to IR signals).

One suggestion is to buy a Phillips Pronto remote (IR) which can learn your curtain's IR signals as well as control your X-10 modules (via IR543).

There are two brand of an IR-controlled curtain system (Makita Motorized Drape System & Drape Boss Drapery Controller) that can support X-10 by way of contact closure using an X-10 universal module.

I don't know if either is what you have, but if your system has some type of contact closure terminals, it's possible to incorporate an X-10 system.

Roland