This can be done.
You will have to use your puclic folders though.
If I repeat stuff you have done, appologies, but I am trying on to overlook anything. I will also assume you have working knowledge of Ex2K and abbriviate the instructions. If you need more detail, I can provide it.
1> Create your task folders from Outlook in your public folders. I would name them something like:
Tasks Brian
Tasks Joe
Tasks George
You will see why in a bit.
2> Assign permissions to the folders as appropriate.
3> In Ex Sys Man (ESM) and right click on each on of the new folders and go to properties. Assign each one a Simple Display Name that is the same as the folder name and uncheck the "Hide from Exchange address lists" box.
4> In ESM Go to "All Address Lists" and create a new address list. Call it Tasks, or whatever you want. Set the filter rules as follows:
Advanced Tab
Field >Public Folder > Simple Display Name
Starts With. . .
Tasks
(that is where the earlier naming convention comes in, so you can get all the folders, with one simple filter and it makes since if you are viewing the GAL.)
Now, whoever is assiging Tasks can assigning them to the public folder account by creating a task in their mailbox, clicking on "assign task" and choosing the Tasks Address list and picking the appropriate folder. The task will be sent via email to the public folder. The person whose folder it is will have to accept the task. At which time the creator will be notified in the mailbox tasks.
It works rather slick. Of course you can always assign tasks through the public folder as well.