HD stands for High Definition and is to do with picture quality
the switch over is the change from Analouge tv signals to Digital
the two are not related,
but to answer your question your tv is neather HD or Digital you will either need to get a digital freeview box or a new tv
heres a freeview box you can buy at Argos
http://www.argos.co.uk/static/Browse/ID71/12108963/c_1/1|category_root|Home+entertainment+and+sat+nav|12108813/c_2/2|cat_12108813|Digital+boxes+and+services|12108960/c_3/3|cat_12108960|Freeview+digital+set+top+boxes|12108963.htm