1. are you sure the non-pnp card is set up to 300,15? (just to recheck yourself)
2. Do you have any IDE devices on your secondary IDE / do you have the secondary IDE controller in your machine turned off. (in bios if it's on the mother board, usually jumpered if it is an external card)? The reason I ask is, it is standard for a secondary IDE controller to use irq 15 by default and if it is, you have an IRQ conflict that would cause your nic not to work. I usually recommend using i/o 300 with an IRQ of 10 for an ISA network card as this is the unwritten "standard" that MANY network guru's have been using since the days of old (well... since there was an irq 10) the only real reason not to use irq 10 is if you have some other device using it (usually a sound card). BTW... if you have a sound card in your e-smith machine; I laugh at you with much gusto HAWHAWHAWHAWHAW! [just kidding]
anyway, those are the two things that sprang from the top of my head to see what was the matter. I'll post any other Ideas if I get anymore. (I'm usually limited to one idea a week, any more than that and the good doctor ups my meds.)