Taktal allows you as a last minute passenger, to purchase tickets which ONLY go on sale 5 days before departure.
This is not a cheap option as you will be charged for the entire running distance of the train as well as some hefty surchrges. It may get you out of a bind though!!
Below are the Taktal rules as of

13-04-2007
   * UNUSED TICKETS ON WHICH NO RESERVATION HAS BEEN MADE :

             *

     Tatkal booking opens at  8AM on five days before of actual date of journey.For example in respect of train leaving on 6th,Tatkal Booking will Commence at 8AM on 1st.
   *

     Instead of full coach being presently nominated as Tatkal Coach, there will be Tatkal quota in each train in 2A, 3A, AC Chair Car and sleeper classes as under:-

               2A - 4 berths per coach
               3A - 6 berths per coach
               AC Chair Car - 6 seats per coach and
               SL - 10% of the accomodation on one coach whichever is less

   *

      In those trains where average utilization of Tatkal accommodation during six months period is 80% and above, accommodation to be earmarked under Tatkal scheme should be enhanced as under

                                                                             
Classes No. of berths to be earmarked where the utilization of Tatkal accommodation is more than 80%
2 AC                                   10 Berths Per Coach
3 AC                                   16 Berths Per Coach
AC Chair Car                      16 Seats  Per Coach
SL                                       20% of the available accommodation

   *

     There will be no separate Tatkal train defined. The unutilised Tatkal quota will get released to waitlisted passengers.
   *

     Provision of I/Card has been deleted on an experimental basis for six months after which this will be reviewed. Zonal Railways may send the feedback in this regard three months after implementation of this scheme.
   *

     Tatkal charges have been revised as under:-

Classes                                                                                Existing (in Rs.)
                                                Non-Peak                                                                                   Peak          
                                          (15 July to 15 September)
2 AC                                           200                                                                                   300
3 AC                                           200                                                                                   300
AC Chair Car                                75                                                                                   150
SL                                                 75                                                                                   150

   *

     The facility of change of name is not permitted on the bookings made under this scheme.
   *

     The reservation under this scheme shall be available only upto the time of preparation of charts.
   *

     For the purpose of granting refunds & issuing TDRs for W/L, the time limit will be the same as applicable for refund of normal tickets.
   *

     The booking under Tatkal Scheme will be done only from originating to terminating point of the train with boarding facility from intermediate station.
   *

     No Concessions are allowed on Tatkal Tickets including senior citizen.
   *

     Trains and classes with average utilization of 80% and above from April to September shall be realized uniform tatkal charges applicable for the peak period.