There are numerous conference rooms in Leipzig, but most of them are quite expensive.
Here are two reasonable priced alternatives:
Die Villa
The Villa is a socio-cultural centre in the city centre.
Besides a colourful cultural programme they provide several rooms for conferences, meetings, workshops, projects and family parties with all necessary equipment.
On request they can also arrange lunch and dinner.
Villa Rosenthal
Another alternative would be Villa Rosenthal with big and fashionable rooms, a basement club which is also to rent and a marvellous backyard and garden. Of course they offer the appropriate catering as well.
Both locations are only a few minutes to walk away from the Sleepy Lion Hostel and the Central Globetrotter Hostel.