Leah137
Firstly, disconnect the aerial from the HD box (then there's no confusion as to what you're recording).
To see which AV channel your HD/DVD plays back on, play a DVD in it and go through your TV's AV settings until you see the DVD contents playing. Then you will know how to view a recording. Also, check the menu on the LG/DVD box to make sure that it is set to record to the HD. I wouldn't record to DVD directly (even rewriteable ones). Record on the HD and then use the DVD for archiving programs/films you want to keep.
Now connect the Scart lead (assuming that this can do input as well as ouput) - see if the HD box has the Scart connection labelled as AV1 or 2. Make sure that your TV is set to a Freeview channel. On the HD box, using the remote, select the appropriate AV channel such as AV1 (the button usually has a small box picture to represent a TV, and/or it will have an arrow going into the box. (My LG HD/DVD, however, has a button labelled AV). As Ethel said, some machines have an EXT button (hopefully not here). Now record the program and then play it back (switching your TV to the appropriate AV channel as found above. Hopefully not too complicated once you've tried it a few times.
The best quality would be obtained by connecting your TV to the front of the LG using an S-Video lead for the picture and the coloured phono leads for sound. This is a bit untidy though - I don't think the LG has an S-Video connection on the back. Your TV might also not have an S-Video out!