I recently had the pleasure of assembling and using one of these
http://www.ebay.co.uk/itm/CHAINSAW-...arden_GardenPowerTools_CA&hash=item53ff95076d I'm not entirely sure how I made it through the day. Scary bit of kit, way too flimsy, way too unstable, an accident waiting to happen.
My recommendation would be to get the biggest, heaviest, most solid lump of a thing that you can find/afford/have space for. Remember the PPE, there's no bonus points for chainsaw injuries, just lots of screaming whilst you bleed out.
Have you already had some chainsaw training? If so then contact whoever your provider was, I'm sure they'd be happy to help. If you've not had any training then the best person to ask to recommend a suitable saw horse would probably be your chainsaw training provider when you do get some. If, however, you think that getting some proper training is overkill then ignore everything I've said so far and just buy the saw horse that I linked to, you won't be needing it for long anyway
All the best,
Stuart.