I know this isn't anything to do with Diamond/Pearl, but I think its good to know for the retro Pokemon gamers
Follow this exactly except when your on yellow avoid the 2 trainers that it uses and get a Abra on the route below cerulean city after meeting bill it still works because i have just done it
http://uk.youtube.com/watch?v=JkF7Xjxn9jc
P.S: It might be lvl 7 but its a nasty one to catch at full health