You can replace it with a normal computer drive, if memory serves me correct those use a Ultra interface. This is what a lot of PS2 users had to do, and I actually fixed a lot of my friends after they dropped HDD support.
I will edit this post when I get home with the actual Drive interface so you can search for a drive.
ah here it is;
http://ps2drives.x-pec.com/?p=list If you need to find out what version PS2 you have use this;
http://www.mod-chip.com/en/ps2version.htm Another late edit, I was right (I called home) They are a Ultra ATA/100 interface drive. If you don't want anything huge you can pick them up for a reasonable price.
Good Luck
Edited, Aug 23rd 2007 5:07:55am by xXBijiontXx Edited, Aug 23rd 2007 5:14:10am by xXBijiontXx