[Long shot]

I have a DLink router in my possession that does not work with Orinoco cards when WEP is enabled. It doesn't flat-out not work. It simply behaves strangely (a lot like you're describing). I had an email dicussion about it with a senior level Dlink tech and he bacically told me that I should buy non-Orinoco cards.

You mentioned that you have a wireless lan. I would try disabling WEP if the machines that are giving you problems are wireless.

[/Long Shot]