Z-transform and ADSL equalizer design

I understand that the purpose of using an equalizer is to shorten the Impulse Response of a channel.In most examples I have seen so far,equalization in done in the Z-domain.Now,I have an ADSL channel response from 1hz to 1.1MHZ.How can I convert this frequency response into the corresponding Z-transform response?In short,how can I design a matlab equalizer for this kind of channel?