How to re-install reclaimed Victorian fireplace?

[PopcornMouseInBoots]

We opened up our chimney breast for ventilation (we had a condensation problem which this has sorted) and would like to put in a reclaimed victorian fireplace for aesthetic reasons (wouldn't actually use it) - but we've not a clue how to go about it.

Right now we just have a hole in the chimney breast with a dirt floor in the fireplace, no hearthstone and a big sheet of cardboard to stop the cat getting in it and using it as a litter tray, ugh We'd need a stone fireback for the fireplace.

The confusion comes in over the best way to install a hearth and concrete the fireplace floor - do we put a granite B&Q-type hearth infront of the fireplace (they don't actually go in the fireplace, do they?), then concrete the fireplace floor to the same height/level as the hearthstone, then place the fireback & fireplace in? Maybe paint the stone fireback black so it doesn't look so out of place?

(I should say, we've tried getting quotes for someone more knowledgeable to do all this for us, but nobody's interested in such a "small" (ha) job, so it's down to us and our shoddy DIY skillz, sob)

Thanks so much...

I had mine done by a prof company and they did what you say, concerete the part which is "the hole". Insert the hearth abutting that, with the fireplace surround on top of the hearth so all flush. See thses You tube tutorials perhaps?
http://www.youtube.com/results?search_query=installing+fireplace+insert&oq=installing+fire&aq=0&aqi=g10&aql=&gs_sm=1&gs_upl=562l4526l0l7223l15l15l0l5l5l0l117l878l8.2l10l0

We had same problem. Original fireplaces had hearthstone set into floor and so ours was flush iuswim, as we didn't use ours as a real fire we just installed our fireplace and then got some small black and white tiles and used them as a hearth, directly on to the floor. Much cheaper than a stone hearth and looks authentic and great (we were also total DIY novices!)