There really aren't that many women in the Original Trilogy.

Think about it. There's Leia, obviously, and then.... umm. It's harder than you'd think.
Let's count the on-screen appearances.

Aunt Beru
The Tonnika Sisters (Cantina extras)
M'iiyoom Onyith (Cantina Extra, and you really can't tell she's a girl unless you read the EU about her)
Does Pink Five count?

There's the lovely Toryn Farr. (Echo Base: "Standby Ion control")
Maybe the space slug is a girl, who can tell?
There are some ladies walking around Cloud City.

Return of the Jedi gets better, at Jabba's palace of all places.
We get Lyn Me, Greeata, Rystáll, and Oola. (All four of which were indentured servants and exotic dancers, and three of which didn't exist until the Special Edition)
Can't forget the sultry Yarna d'al Gargan.
Sy Snootles
And last but not least, the always respectable Mon Mothma.
By the way, if anyone knows how to check if an Ewok is male or female, please tell me. --On second thought, I don't think I want to know.

Quite the list there. Three movies, an entire galaxy, and a lot of the women are sex objects for a giant slug. There many more women in the prequels, both civilized and in the underworld, but just looking at the OT, it's surprising.

What men are there, off the top of my head? Han, Luke, Vader, Tarkin, Piett, Veers, Palpatine, Greedo, Bossk, Dengar, Boba Fett, Zuckuss, Chewie, Obi-Wan, Yoda, Wedge, Biggs, Riekan, Ackbar, Madine, Lando, Nien Nunb, Bib Fortuna, not to mention the many named Cantina and Jabba's Palace male extras. Which list is more impressive?

Why is this?
Well, the OT is, in a nutshell, about Imperials, Rebels, and scum and villainy. Imperials? Palpatine's new order is sexist. Case closed. Rebels? What we see of the Rebellion is the warlike side. We only really get to see rebel warriors, which, are generally more likely to be male. Scum and villainy? Same thing. It's more probable fringe types to have male personalities (or have female slave dancers).

(The last two are generalizations of course, but explain the trend, albeit not to the exclusive extent that the movies seem to portray).

What of it?
Is this sexist? Well, there's sexist and then there's sexist. There's a truthful distinction between tendencies of males and females, but recognizing that is, to some, sexist by virtue of the fact that it says there's a difference. Then there's prejudice and judgment passed on someone because of their sex. For the Imperials, that's exactly what they're doing, it's not GL being sexist. For the fringe, they're doing it too, personifying females as sex objects. The Rebels, though, there' s the warrior explanation, but that's not quite as satisfying. So do I think the OT sexist? Not really, but there's still more to consider.

I think that George Lucas made those choices to maintain a positive perspective of women. That's sexist, in the overly protective way, but that's far from the worst kind of sexism. Women in the OT just aren't associated with the bad guys in a willing fashion. And they're also not the warriors and brutes that men are. Remember, "Wars no make one great." This isn't the Klingon Empire, being on the front lines isn't a matter of greater honor or anything.

Conclusion
There's some sexism. The kind of sexism that stems from chivalry, which is also the kind of sexism that garners the most hypocritical thoughts. I'm interested in what you all have to say about the sexism of the OT movies. Especially since I'm a guy, and as such, don't feel I have as much a right to make any final judgments on my own here.

PS-please point out any and all visible females from the OT that I missed, I've got to be missing some.