Wow, 2kv @ 900mA???!
In order to use a 'regular lightbulb' as a plasma globe, anything from 12-15kV + would do, like the output from a typical >modified< flyback transformer design. I have no idea why you would want 2kV@0.9A at the output..its not enough voltage for the plasma globe, would kill you, and you won't get it from a flyback. You need maybe 5mA DC at the most, have you tried using a simple cockcroft-walton multiplier? Word of warning, 2kV at anything over 10mA (DC) is dangerous enough.
Heres a link to a legend of the HV world:
www.electricstuff.co.uk
And of course, powerlabs:
http://www.powerlabs.org/plasmaglobes.htm
A regular light bulb wouldn't be a proper plasma globe, different gases at different pressures. And the largest flyback I have from a 22" crt monitor only kicks out 3kV, but it has a built in rectifier diode on the output, and I haven't modified the primary windings at all. Do you have a 12v supply capable of 3A? I would have thought a single 3055 T03 transistor would do (or a mosfet would be waay better) on a fat heatsink.
One way to ensure you get a LOT of voltage on the output (as opposed to just the step-up winding ratio) is to use the flyback transformer in....er..'flyback'
If you hand wind a feedback winding, and use that to switch on/off two transistors (LOADS of schems on the web of this) then the primary develops up to 4x the power supply, which in turn is stepped up. Although all these designs rely on the use of an old flyback, without built in diodes, and a custom primary winding.
My two cents,
Blueteeth.