Hi spdrtanzil --
There's still a Netware 4.11 base out there, but I believe Novell has retired the CNA/CNE track for that product, so that's pretty much out.
You can still earn a Netware 5 CNA by passing the Netware 5 or 5.1 Administration exam (I'm pretty sure either exam gets you a NW 5 CNA; there's no separate 5.1 track of which I'm aware). There are certainly plenty of folks out there running those, so 5/5.1 wouldn't be a bad certification to pursue.
Of course, Netware 6 is pretty much brand spanking new. If industry pundits are correct, it could be Novell's ticket back into a serious share of the network OS market. If they're right, Netware 6 CNA could be a good ticket for your future prospects (when it's available; it's still "coming soon" on Novell's site). Of course, a Netware 6 CNE is going to carry considerably more weight than a CNA, but there are also several more exams.
Also, because it's fairly new, there aren't as many Netware 6 self-study materials available as there are for 5/5.1 (although the David Clarke CNA 6 study guide is due out mid-January 2002). It might also be a bit tougher to get the hands-on you need to be sure you really know your stuff. You can get a 3-client version of Netware 5 or 5.1 with the David Clarke CNA study guide.
I guess that means that if you're willing to hold out a bit and see where the market heads, you might do well to go for the Netware 6 CNA. Otherwise, I'd say play it safe and go for 5/5.1.
(P.S. I'm not particularly fond of the David Clarke books, since I can't really stand his superhero storyline writing style, but the info's good. YMMV.)
Hope that helps,
Don