IE8 and embedded videos on some sites

Hello,
I run IE8 on 2 different XP H.E. PCs and 1 Vista Home Pro. laptop.
On 1 of the XP H.E. PCs IE8 doesn't show embedded video on some websites (on
some other websites they are showed and played correctly!). At the moment I
have to use Opera to see such videos on this PC.

What can the possible causes be?

I have read some past threads (problems from antivirus softwares,
deactivated browser extensions etc) but the 2 PCs running XP had very
similar configurations and I have this problem only on 1 of them...

One example of webpages where I have this problem is this:
http://www.telefonino.net/Nokia/Vide...Nokia-N97.html

TIA