I know it's been a while since you posted your question but i just bought a 20 gig iriver on woot and am curious to know if the hard drive is as easy to swap out as my Archos.
It turns out that while the Archos is a standard 2.5" notebook HD the iriver is a 1.8" HD which I'm not familiar with. Also Hitachi/Travelstar make the drive with the pins at the end or on the side. I would assume that the pins for the iriver are on the end.
Have you had any other replies or broken into your unit on your own?
http://reviews.cnet.com/40GB_4200RPM...-30910718.html
is the address at cnet where they review the drive and this:
http://www.memorylabs.net/40lahdd1noha.html
is where you can buy them.
let me know if you get into your unit. the Archos i bought was a 5gig unit also and you're right, just not enough room so i found a site that diagramed how to crack it open and swap out for a larger HD. Now I Have a 20 in and carry the 5 as a back-up.
luck,
rob