First off, I'd just like to say THANK YOU to evilsperm for introducing me to Posadis, it's exactly what I've been looking for.
Secondly, while using Posadis, I noticed something interesting. As soon as I tried to connect to the playstation network on my PS3, I looked at my PeerGuardian on my computer that is running Posadis, and it was blocking a bunch of connections to Sony. This was preventing me from logging in on my PS3. There were about 3 different IPs it was trying to connect to, and after I allowed just 1 of them, I could connect on my PS3 just fine. For those who are having problems, you might want to look into this and see if your problem is caused by something similar.
-=Edit=-
Now that I'm using this some more, I see that I have to allow all the IPs, or else the PS3 will hang trying to load certain pages.