Q How do I install HD loader to my memory card (DMS3 Devmode 1) ? 

A Obtain HLOADER.ELF of size = around 640KB 
Now create a CDR containing the following 

HDLOADER.ELF 
SYSTEM.CNF 

Using notepad edit SYSTEM.CNF, and copy and paste the following in: 

BOOT2 = cdrom0:\HDLOADER.ELF;1 
VER = 1.0 
VMODE = NTSC 

INSTALL.CNF - Again edit this file with notepad and copy and paste the following in: 

HDLoader 1.0 
mc0:\BOOT\HDLOADER\HDLOADER.ELF 
_MKDIR mc0:\BOOT\HDLOADER 
_COPY cdrom0:\HDLOADER.ELF;1 mc0:\BOOT\HDLOADER\HDLOADER.ELF 

Double check your CDR contains the following: 

HDLOADER.ELF 
SYSTEM.CNF 
INSTALL.CNF 

Then using your favourite burning software burn the disk in Mode2. 

Tip, if you'd like your PS2 to boot straight into HDloader rather than DMS's explorer, rename HDLOADER.ELF to BOOT.ELF along with all references to the file in SYSTEM.CNF and INSTALL.CNF 

Trouble shooting, if your disk will not boot in your PS2, try adding some dummy files to your CDR.