Best to use HDL Dumb, you run the HDLD elf on your PS2 and the HDL Dumb on your PC connect the IP's and click connect on your PC. Transfer the ISO's over that way.
Just make sure you PS2 has a network configuration file either on your Memory card or on a USB stick.
Another thing to note is that you will need to configure your network settings or your PS2 will be set up as 192.168.0.1 and that will probably conflict with your router....
If you have any questions I can help, I struggled over the past 2 days setting all this stuff up myself lol
(You can also use the built in HD Network transfer tool built into Open PS2 Loader but it runs about 200-400K a second slower than the old dos looking HLDL elf.)
Edit: If you have a way to run Open PS2 Loader, do that go into the configuration and find the network settings, if there is no network configuration file it will auto make one, if there is already one it will change it to what ever settings you want. I set mine up as 192.168.0.15, then I put that IP address in HDL Dumb on my PC and just click connect its super easy.
Edit 2: Also you won't be able to just FTP over games to the PS2's hard drive the drive is formatted in some weird way in fact to transfer games to it even connected to a PC you have to use a program called Winhiip.