I'd agree with Kossy.
They're ok if you've got great water quality. NO ammonia or nitrite and little (<25 mg/l) nitrate. Check the shop's water parameters too, i.e Temp., pH, GH and KH and try to match these if the Discus are healthy in this, if not then don't buy from that shop. Ask to see them feeding at the shop too, they should come to the glass when approached and feed straight away. They need a few small feeds daily rather than one or two larger one's as they are fussy feeders and left overs will pollute.
If you buy juveniles (less than 3 or 4 inches), you will need a shoal of 5 or more to reduce aggressive behaviour. You should ideally allow 10 gallons per adult discus, so if you intend allowing your juveniles to grow to adults then you'll need a big tank.
I was going to take the plunge myself but took the easy option and know have Angels, Rams and Tetras in an Amazon Biotope.
There's some great Discus websites out there, do the research and you'll be gifted with the knowledge to look after these beautiful fish. Good luck mate, let us know how you get on.