console only is just the box - you'd need a PSU, video cable and gamepad to make it functional, plus a headset, hdd and network cable / wifi adapter to make it fully functional!
I looked at this, and found it wasnt worth it - Blockbuster Video had an xbox premium 60GB with halo 3 and PGR 4 for £159.99, I managed to get them to refund both games for the RRP(!) and got a wifi adapter (total cost £134.99).
Even on ebay you'll pay £80ish for a decent console, plus £50-60 for the HDD and lord knows what for cables and pad (probably another £30-40) so I reckon its not worth it.
More importantly you've gotta ask why is someone selling just the console? They dont come in the shops like that, however they do come more easily out of people's front living rooms if you dont take the cables as well - i.e. stolen - if thats the case they'll be perma-banned from xbox live. The other alternative is that they are repaired (professionally or by an amateur from the Red Ring of Death fault, either way I wouldnt want one).
Save yourself some bother, buy a new one, get a warranty (3yrs now from microsoft) and a free xbox live trial with it....