Prerequisites for SDNet are a Vampire card (V500 or V600), along with the Gold2.5 release. In terms of additional hardware, a suitable Micro SD breakout, a 3.3V ENC28J60 module and some easy soldering are required.
Please be careful with the breakout. Many MicroSD models use a thick PCB that will quite likely destroy the SD slot. In my experience, the plug from cables sold as "TF to micro SD card Extension cable" on fleabay worked well. Reminder: The soldering is easy. Take the time saved on soldering to grind the edges of the breakout connector into a smooth feel.
More information, pin-outs, driver, test tool and associated sources (GPL) can be found in the following archive: http://www.apollo-accelerators.com/files/sdnet0.8.lha
Disclaimer: This is a DIY hardware project for experienced personnel only. The information is provided as-is, without warranty of any kind, expressed or implied, including, but not limited to, the implied warranties of merchantability and fitness for a particular purpose.