Leopard still won't auto sleep!

Alrighty,

First, I have a 2.0ghz CD Macbook with 1GB RAM. I recently did an erase and install update to Leopard. Since then, I have not been able to get the computer to put itself to sleep. I can manually tell it to sleep or shut the lid and that works, but it won't auto sleep.

I have tried:
-deleting all HP files
-Resetting SMC
-Disc utility stuff

Nothing has fixed the problem so far.

Here is the weird part:

If I restart the computer with the ethernet cable unplugged, the computer will sleep fine. If, at any time, I plug in the ethernet cable, the computer will not sleep...even if I then unplug the ethernet cable. I really don't feel like making a launch daemon to solve the problem and I don't feel like downloading third party software to fix the problem.

Basically I'm just afraid that the hard drive is getting unnecessary wear and my battery life is terrible if the laptop is left open and not charging. I'd be perfectly happy to hear that this is an OS problem and will be fixed next update.

Please help! Thanks!