If you had an existing DVD recorder with an analogue tuner (or bought one on eBay) it would be possible to record Freeview programs (using the 'Line In' facility) by taking the signal from a Freeview set-top box or from a TV with built-in Freeview. However you'd only be able to record what you were watching. (You wouldn't be able to watch one digital programme while recording another because you'd only have one digital tuner in your set-up). However getting the connections set up properly can be rather awkward.
To record one digital programme while watching anotheryou'll need a set-up with two digital tuners. The simplest way of achieving this is to buy a DVD recorder with a built-in digital tuner and to use it with a Freeview-enabled TV (or with an analogue TV and a digital set-top box).
As VHG suggests, almost every new DVD recorder currently on sale will have a digital tuner in it anyway.
Chris