I did a quick "specs" on your model and it offered that an optional HD was 80gb. It also mentioned ram could go to 1gb vs. the std. 512mb.
XP is XP, however again from the specs it made the mention that it was XP Tablet OS. So, I suspect that some special attention was given at the time for tablet use. If in fact the XP is buried in memory stick, then it's bound to be locked with no user changes unless somehow accessed. Which brings up the special situation of these tablet releases, it's no longer provided in this way. later model rely on access to the OS and whatever updates required to keep up to date.
Flat cable, I would have to view it more than anything else. if access to schematics it should explain what it is. Probable use is static or grounding strap. It may merely need to touch the HD or be an area that allows to drain static build-up, etc.. That's only a guess.