Looking for a postdoc: How to approach professors in a conference
Your current work shows what you managed to accomplish so far - which is a first estimate on how you might perform in the future. Therefore, talking about your current work is not bad. 

If the interesting people are visiting your poster, everything is easy: Just ask them how they like your work and tell them you are looking for a postdoc position. Either they catch the ball or they don't ;-). If they are interested, just ask whatever you are interested in, or, if they are short in time, ask them when you could talk (perferably at the conference). Maybe you can meet for lunch / dinner / at the conference social event, coffee break, ... depending on the social interaction options at the conference (don't ask for dinner / lunch if it is not part of the official conference program).

If they don't come to your poster: Try to use the social interaction options mentioned above to approach those professors. Tell them why you would like to talk to them (why this group, what are your itnerests, ...). Invite them to visit your poster so you can show them what you did so far.