Hi! i am from argentina, my english is not very good but i try to explain my problem the best posible i can.

I have an older NCR computer (model 3501) and i have modified it to have a CD-ROM and Hard Disk drive (before that the machine only has one IDE power conector for one device, CD-ROM or Hard Disk but not the two at the same time) i use it for music and DVD movies but i can't make the on-board network card to work on Windows 98 Second Edition. The system detects it as a "AMD AM2100/AM1500t and compatibles" and it ask for irq, dma and address for the network card because it has problems with other devices and i select other values but it don't work so i select the conflicting values and deactivate the other devices and again it don't work.

Now i don't have idea of what to do and i don't have a free pci port for another network card (the only two PCI are ocupied with a Sound and Video Card)

It has been awhile since I messed with 98se...but you still have to install the drivers for the NIC card to work. Have you downloaded and installed the drivers for the card....even if it is built in the drivers are installed separately

It's been a while here to but I think this sounds like what I used to run into, especially since you modified the hardware configuration.
Some older hardware required specific IRQ and Memory address space. If you have 2 conflicting ones (trying to use the same IRQ for example) you need to change one. Look in the device manager for But some devices will only work correctly with certain values.

Try changing the value (IRQ or DMA setting) of the added hardware (likely a modem or card for CD)
Or try removing them and see if it clears up the resource conflict. Then you will know the network card works, and add one device back until the conflict re appears and you will have you answer as to what device is causing it.

Computer System Resource Information

It could also try turnig off IRQ steering.
Windows 95/98 Support-irq steering

SquirelandMoose reminded me of an old trick that I used to solve this type of issue....

If you have an old modem card in the computer.....install it in the furtherest slot away from the CPU (or just remove it and leave it out)

Install the NIC card in the closest available slot closest to the CPU....the video card if it is PCI can be moved to any other available slot.....If AGP then there is no need.

The two communication devices always seemed to get in the way of eaxh other and caused the conflict...

I have solved the problem. The Sound Blaster 16 PCI sound card was changed with an ISA (Crystal CS4236) and a Realtek Network card (RTL8139A) in the free PCI port and now i have internet but i still want to make the on-board lan port to work.
The lan port is not a NIC, is an AMD AM2100/AM1500t (I don't know if this is correct, Windows detects it as a AMD lan port and the damn "Everest Ultimate" detect it only when the drivers are instaled)