You can buy a Freeview box that will work with your TV but you need to take care to ensure that you buy the right type.
All Freeview boxes have an 'aerial out' socket on the back but, in most cases, this only provides 'RF loopthrough'. (That means that the signal which comes out is exactly the same as the one which went in. You can't use it to watch digital channels).
What you need is a box which has a built-in 'RF modulator'. With this type of box, you connect the 'aerial out' socket to your TV (using an aerial fly lead) and then tune in a channel on your TV to receive the signal.
This website tries to maintain an up-to-date list of all available Freeview boxes but suppliers' stock situations change so quickly that you can't always find the relevant models by following the links. (Boxes with a built-in RF modulator are indicated by 'Mod', in a blue rectangle, underneath the picture):
http://www.radioandtelly.co.uk/freeviewreceive rs.html
Alternatively, you can buy a separate RF modulator (to go between a 'normal' Freeview box and your TV), from Maplins, for �29.99.
Chris