I think I am sorted now, I have several boot CDs which load the exploit and I have just copied the ISO of one of them to the HD so I can load the exploit from there after starting the PS2 with HDadvance.
Gave up with DMS HDD as it wouldn't FTP to the HD, and as has been said, I can just copy game data from the MC to the __BOOT partition which I can see from uLaunchELF.
One thing I don't understand - if I load the FTP server function in uLaunchELF and connect to it from the PC (I use CuteFTP) I can copy game data from the MC to the PC, but I get really weird failures if I try to write them back to the PS2 HD. I am obviously doing something wrong here.
Cheers and thanks for the help