simple just do this:
take hdd explorer and install it (you can launch from lan and it should say partial installaion is ok in that way)
then use ftp or ps2os directly and go on __boot partition
erase boot.elf if it's there, and copy ps2os on that partition renaming it as boot.elf (all undercase). reset your ps2 with start pressed and here you are your ps2os from hd, other way is installing a loader on the mc but it's less direct.
then you can go on dms config and select autoboot on dev.olution 2 and ps2os will start automatically at all boot (if you don't select something different on the controller)
ps2os betatester, ps2tools codev, hdldump frontend dev
6 sony mc w/ps2os 0.2.4, hdl, ps2rmp1.50,ps2mp3...
na+hd maxtor diamondmax 7200 120GB
PS2 SCPH-30004R V6 ÐM$3 V2 firm 2.4 B.4
PS2 SCPH-50003 V9 ÐM$4 PRO firm toxic os 0.1