Hi everyone!
Once again, many thanks Gnoboot for your work!
I managed to upgrade to the DSM 5.0 4458 with the gnoboot 10.3vfat image on a HP N54L. Before, I had a native install with DSM 4.3 3827.
So far it works pretty well. No loss of data. The only things is that i don't see my shared folders in the File station, eventhough settings are still the same as i had on the previous DSM and i can access my shared files... I guess i'll have to go through the settings again.
As soon as i find time, i'll try an install with esxi 5.1. Will let you know how it goes.
Once again thank you very much for your work all of you
Edit: problem solved. It was a user right issue.