For tatkal booking you can follow some rules and try tricks.These are from my experience
1.For tatkal booking log in to IRCTC site atleast five minutes before 800 hrs.After giving names of from & to stations and date of journey and keep on refreshing the site by clicking on find the trains by giving general quota option(not by giving tatkal selection).This is just for updating the IRCTC server time on your computer.Once IRCTC server clock just crosses 0800 hrs, immediately change quota selection from general to Tatkal and click find trains.Now........
2.Never use...
more...

IE browser for booking tatkal ticket, it has more filters on it, by the time your computer gets connected to IRCTC server(between 0800 to 0810 hrs) only W/L will be left.Even if you login in thru IE browser, the next step if "service not available" message appears ,you will have to relog in, enter all details again.By this time there will be no scope
3.Instead of internet explorer use Opera, firefox or google chrome.I use Opera.
4.If you are booking from home, allow the browser to save your user name and password (later you can delete if you want)for IRCTC site.By this you can speed up the log in time
5.In Opera, firefox and Chrome, during any stage if "service not available" appears, just click go back(reverse) arrow you will get back to last menu with all details filled(this is not there in IE, there journey details need to fill again)from there you can further proceed.This is an added advantage.
6.Now assume you are lucky and proceeded for payment option, in the card verification/authorisation process if browser hangs and not proceeding further, what you have to do is again click reverse arrow(it will be written on site never refresh/finger while verification/authorisation is under progress)now the process will be completed and your ticket will be booked.If you really want tatkal ticket you can take this risk.
These are my experiments with tatkal booking.If curious you can also try.