How to print in duplex mode?

[Mikhail Teterin]

Hello!

I'm trying to use less paper by printing on both sides of each sheet.

The printer is capable of duplex printing, but all the postcript I send to it 
ends up printed single-sided.

The original PS is generated by a web-browser. I then try to use enscript's 
pstops utility, but can't figure out its page-specification language :-(

Would someone have a ready example:

	pstops 'MagickSpell' input.ps duplex.ps

Thanks!

	-mi