You have two solutions: export your animation in flash from poser with no background lines, ( i include a blue or green color, i don't know if it is usefull) ). You open flash,create a layer, and import your swf.

2: you export your animation in avi with a blue our green background, and no lines, then you use "after effects" only to tranform your avi on to swf. Then you open flash, and import your swf.
i hope you will succeed!