Hi, I'm going to do the same. See http://forums.rockbox.org/index.php/topic,42901.msg218180.html#msg218180
I wonder why you failed with yours. What disk did you use? Not every HDD will work 'cause some H10 HDD chip controller issues.
I tried it once with 80GB Samsung and it worked fine (and is still working, but 80G is far too small for me). Now I'm heading for 240GB Toshiba 2431GAH and AFAIK it SHOULD work.
You can format HDD directly in H10 or using an adapter ZIF 40 CF USB 1,8 PATA IDE Micro 50 like this one:http://allegro.pl/adapter-zif-40-cf-usb-1-8-pata-ide-micro-50-a039-i3066200299.html
(this auction is Polish but you surely find it elsewhere, the picture tells all) - it costs less than $8 and I use it to check HDD and format it in FAT32.
THERE ARE MANY malfunctioning HDDs on the market. Lately I got very cheap one ($8, no laughs please) and it burnt an adapter. It could happen to your H10 too. Thus I would recommend to buy a new one from reliable seller.
IMHO the one and biggest problem is to properly insert HDD tape into ZIF connector of HDD - iRiver tape is somehow thick and you need to be careful. I broke one tape already and had it replaced.
PS. If you like you can contact me directly through mail: firstname.lastname@example.org