Both my wife and I have an IRA where the contributions are on an after tax basis. It took a lot of work on my part to properly model this with the current version of ESP, and it would be very, very helpful if the program would handle the contributions and distributions from these after tax IRAs. I am certain that my wife and I are not the only people with this type of IRA.
The 401-k after-tax balance should be entered into the "ROTH accounts" totals based on prior questions. This does address the tax exemption on withdrawal but does not address the taxable gains since ROTH balances are tax exempted.
For after-tax contributions, I'm assuming they are also entered on the contribution tab as "ROTH" since contributions are not tax exempt. Again, the gains on these contributions should be taxed upon withdrawal.