Your script store file structure:
 \\mydomain.com\SYSVOL\scripts\posh\ - the base folder for your posh runner
 \\mydomain.com\SYSVOL\scripts\posh\supportScripts - contains all of your init scripts
 \\mydomain.com\SYSVOL\scripts\posh\domainScripts - contains all of the scripts you want your client to run

Security considerations for Unrestricted exeucution policy:
 1. Set the Unrestricted exeuction policy in your domain [user settings]

  ADM Template: http://www.microsoft.com/downloads/details.aspx?FamilyID=2917a564-dbbc-4da7-82c8-fe08b3ef4e6d&DisplayLang=en

  [HKEY_CURRENT_USER\Software\Policies\Microsoft\Windows\PowerShell]
  "EnableScripts"=dword:00000001
  "ExecutionPolicy"="Unrestricted"

 2. Add your script store location as a trusted IE zone [user settings]

  -Navigate through User Configuration / Windows Settings / Internet Explorer Maintenance / Security.
  -Right-click Security Zones and Content Ratings in the right-hand pane and press Properties.
  -Select Import the current security zones and privacy settings. If prompted, press Continue.
  -Press Modify Settings.
  -Select Trusted Sites and press the Sites button.
  -Type the full URL of the site you wish to add and press Add.

  In this case the URL is: file://\\mydomain.com\SYSVOL\scripts\posh

\\mydomain.com\SYSVOL\scripts\posh\poshRunner.bat:
%systemroot%\system32\windowspowershell\v1.0\powershell.exe -NoLogo -NoProfile -Noninteractive -Command ".'\\mydomain.com\SYSVOL\scripts\posh\poshRunner.ps1'" %1

\\mydomain.com\SYSVOL\scripts\posh\poshRunner.ps1:
 if ( -not $ScriptToRun -eq [System.String]::Empty )
{
  Write-Host "Args: " $args;
  $scriptsPath = split-path $myInvocation.myCommand.Path;
  # define your variables, functions, etc... before running your client script
  . $($scriptsPath + "\supportScripts\Init.ps1");
  . $($scriptsPath + "\supportScripts\Variables.ps1");
  . $($scriptsPath + "\supportScripts\Functions.ps1");
  & $($scriptsPath + "\domainScripts\" + $ScriptToRun);
 }
else
 {
  Write-Host "No Args!";
  break;
 }

\\mydomain.com\SYSVOL\scripts\posh\domainScripts\PoshWasHere.ps1:
 $fname = $env:USERPROFILE + "\poshWasHere.txt";
 $stamp = (Get-Date).ToString();
 Add-Content $fname $stamp;

Now, in your GPO you can add PS1 logon/logoff scripts:
Script Name: \\mydomain.com\SYSVOL\scripts\posh\poshRunner.bat
Script Parameters: PoshWasHere.ps1




Some script wackiness: http://www.hanselman.com/blog/CommentView.aspx?guid=6a30d72b-4c9d-4141-b44d-9b074caa833f