I would think that just about any knitting machine would be able to handle scarves since they 're generally long rectangles. However, I'm not sure about using a machine to knit in the round for a hat. Perhaps it could be knitted flat on a machine and then seamed up by hand? It's certainly worth asking a knowledgeable person about!
One other place you might check for information on knitting machines is in knitting magazines. I know Knit 'n Style has reviewed knitting machines in the past. However, with that said, I wouldn't recommend getting a subscription to a bunch of knitting magazines just for that purpose. Instead, perhaps you could browse through some copies at your local library or even flip through some at a news stand.
Good luck in your search for a good knitting machine. I hope you can find something you enjoy and that fits your budget and needs perfectly.
If you are able to make some items via a machine, please do post some pictures for us to see. Even though most of us here hand knit, we are very much interested in all things knitting!