Which poser figure are you trying to do this with? Some of them have a specific transparency map which will do this for you when applied via the material editor. I usually select the eyelash mesh (one of the head series) and set the colour to black in the material editor. Then you set the little ball in the transparency slot (usually the first one). A texture will pop-up in the corresponding slot on the right. On that texture, click the P button (sets it to a photographic or image texture). Click on the edit button and it will take you to the image manager where you can load the transmap you need for the lashes (if there is one for your figure). Back in the material manager, click the little down arrow beside the slots on the right and select Blend Transparency. That should do it. I think Rochr has a good tutorial for this on his website.

Pass no temptation lightly by, for one never knows when it may pass again!