Straight from the R&D labs of IBM's "Problems That Don't Need Solving" Dept, we have a patent for an instant messaging program that displays a male, female or "can't decide" avatar, based on your name.
Even if the system worked flawlessly - even if it could somehow cope with Andy, Daryl, Francis, Jo, Leslie, Mich, Robin and Terry - it would still be 100 per cent useless. Who wants an IM program that forces you to use a specific avatar? How hard is it to just ask someone which gender they would like to use? And who just has a simple first name as their IM login anyway? All the people in my chat contacts lists have names like XX_$t@lker99 and gravelpit. This is a frivolous patent for an unworkable technology to solve an imaginary problem. Coming soon: a system that guesses your name, based on the avatar you choose.
If you must take a stab at guessing someone's gender online - and I reiterate that this is absolutely not a remotely worthwhile endeavour - then it's really quite simple.
Just assume they are male.