Yes, the 8.8 profile migration tool will not work on Windows Vista or 7. In 9.0 it is fully supported, and works great.
Assuming you can get to 9.0, here is a document that walks through most of the XP to 7 migration process.
That should be a good resource, and any improvements or feedback received will go into making that document THE go to resource for an XP to 7 migration plan.
We are planning to upgrade to 8.8 SP4 but we are not sure at all for 9.0.
Is there any other way or tool able to perform such operation ? in Freeware if possible ?
I have tried the "Windows Easy Transfer for Windows 7" tool but it doens't seems to work.
At this time the Profile Migration tool from LDMS 9.0 is not planned for back-release to 8.8. I do know that you can use Microsoft's USMT utility, and the XP to 7 migration I linked to above includes a document that shows how to use an old version of that tool.
I've never personally used it, but I do know that a lot of people feel that it is a very good method for migration.
Just for help in finding it, USMT = User State Migration Tool.
Let me know if that helps!