Wow you've chosen quite a handfull for your first Amiga in 10 years!
If you have installed OS4.1 then use the extra's installer to install Ranger, you can use that to see if what is connected to your Mediator is picked up.
The only PCI network cards that works with OS4.1 are cards based on the Realtek 8029 chipset.
Have a good read of the FAQ's and this blog:
http://www.hd-zone.com/ and
http://blog.hyperion-entertainment.biz/Good luck with your project.
Steve.
