I also have a Orinoco card. (But it's gold.) I don't remember if I ever had any trouble with the Orinoco drivers... But I did the following for my PB3400c:

http://www.alksoft.com/projects/unsupported_airport.html (Requires Mac OS 9.)

I think I did it mainly so I could use the laptop as a wireless bridge. Because AirPort includes the startup extension of IPNetRouter. Called AirPortAP. All I had to do was replace the config file for AirPortAP with one made in IPNetRouter and I had a free copy of IPNetRouter. But then much later I found out that at the 10 year anniversary they gave out free single user registration codes.

If you haven't already you could try to upgrade your silver to gold:

http://web.archive.org/web/20021015005610/http://www.paris-sansfil.net/index.php/UpgradeSilverToGoldEn

You could try disabling WPA2 temporarily to see if that is causing the flickering.