Frederic,
I went and looked at the post you mentioned on EE, and perhaps they just do not realize yet that this is a free upgrade if your maintenance is current. What you get with the free upgrade, is the Sametime Server and online awareness and IM within the Notes (including any Notes Apps) and iNotes Clients. Now what you do not get with this free upgrade is the use of the Sametime Connect client, or the Web Conferencing Server. For these two components you must purchase a client license.
Please take a look at Ed Brill's BLOG for more information http://www.lotus.com/rw/eblog.nsf
Hope this helps.
Regards
Sean T.