Need help finding Apom? They are rare in Diamond/Pearl, but not impossible to get.

[edit] Steps

Go to Floaroma town.
Head north through the field of flowers. In the top-left of the field there should be an exit. Go through it.
Talk to the man directly north, and purchase some honey from him.
Run east. There should be a gold-brown tree standing alone. Activate it, and agree to smearing honey on the tree. Leave and do something else for 6 hours.
Return after 6 hours. If the tree is rustling (shaking from side to side), activate it. You should enter a battle. Chances are you will be facing a Combee, Burmy or a Pineco.
Repeat the previous steps until you get an Aipom. Catch it in the usual way.

[edit] Tips

These Pokemon are rare. It is probably quicker to trade one from a friend, or obtain it via dual-slot.
There is more than one honey tree in Sinnoh. There are two east of Floaroma alone. Theres nothing to stop you smearing honey on multiple trees. This will speed up your hunting a lot.
If you are impatient like myself, after putting honey on the tree(s) you can simply turn off your DS, restart it, and move the clock up six hours. Start the game and the tree will probably be rustling. Try moving the clock back and forth until you find one. After catching your Aipom, remember to change the clock back(I don't know if it would be smart to play it before the time your game had when you caught it.
Or option 2: ACTION REPLAY!!!!