Future-proofing for a new high-spec system

Hi all,

I've decided the time has come to buy a home cinema system, and I'm the
kind of person who's going to save up for something stupidly good if
he's going to bother at all. After a bit of reading, I'm reasonably
happy with the pros and cons of the major technologies, but I don't know
enough about future-proofing yet to be confident spending the kind of
money involved. If anyone can offer advice on this, that would be great.

At the moment, I'm tending towards a pretty large DLP-based system,
which will be used with a hard-drive/DVD recorder and probably a 5.1
speaker arrangement. I've got my eye on the Sagem Axium 50" model, which
had by far the best image quality when I saw it set up at my local
store. However, I've seen reports of some issues with early versions,
and later reports don't seem clear about whether they've been resolved now.

I'm also not sure I understand the implications of the connectivity and
HDTV spec: if the unit is only able to do 720 lines, how will it handle
any 1080-line video in the future, and is any technology (either
broadcast or prerecorded) likely to actually provide this quality within
the next few years anyway? Is the lack of HDMI, which seems to have
started appearing on other high-end sets recently, a liability?

Finally, I'm not sure the comparison was entirely fair: rumour has it
that Sagem engineers insist on setting them all up for optimal display
in the stores, while other high-end DLP and plasma sets might just be
plugged in without any careful configuration, so I'd be comparing
against sub-standard results on other sets. Any tips for checking
whether other good quality sets are actually set up optimally in the
store? Failing that, does anyone know a specialist store within
reasonable range of Cambridge where the staff actually know what they're
talking about and hardware is likely to be set up properly, so I can get
a genuine comparison between the different kit?

Thanks in advance for any help,
Chris