Expense account for mortgage principal

[Jim]

Hi,

I have a scheduled transaction for my mortgage payment that looks 
something like this:

Interest     Expenses:Interest Mortgage     25.00
Tax          Expenses:Taxes:City Property   25.00
Principal    Liabilities:Loan Mortgage Loan 50.00
Payment      Assets:Bank Account                  100.00

This seemed to work fine until I ran an income/expense report.  The 
problem I'm seeing is that the Principal doesn't show up as an expense.  
I'd like to use this report as an indication as to what my cashflow 
'really' is.  That is, I'd like to see how much I'm really coming out 
ahead (or behind) every month.  I'm thinking that the solution is to 
create another Expense Account for principal Payments.

1. Is this acceptable accounting?
2. If so, How/Where should I place the other entry to balance the 
principal payment?

I have the same issue for my 401k witholding.

thanks,
Jim