Simon, there is a post asking this question about every 3 days on here, not that your wrong in asking but if you trawl back through the lurcher posts, you'll see 'em, with many differing answers. It's worth a read. Gather all the info you can and make an informed choice.
As for my two penneth worth, first off, don't be too hasty, don't jump at the first thing you see, do your homework... Look to parents of average size 22"-24", that are well worked, make sure the parents are of racy type and you won't go far wrong.
Best of luck.