The beaming/IR features of most pdas I know of is pretty weak. When I use IR to hotsync mine with my laptop, the IR ports need to be facing towards each other, and not too far away for it to receive.
That said, if someone beams something, everyone within range with Beam Receive set to ON will receive it.
Interestingly, there is a company that sells a "turn your PDA into a remote control" kit that boosts your IR output signal well enough to reach the TV on the other side of the room, so if you got one of those, perhaps you could set yourself up as a sort of PDA spam broadcaster... but I don't know of any IR reception boosters for stealthily intercepting a transmission...
I've only used PDA-to-PDA beaming once, but I was not asked to give the recipient's ID... Perhaps some specific secure applications might require that information to beam their info, but generic Palm OS beaming doesn't seem to ask anything about the recipient.