• http://kb.mozillazine.org/Running_from_a_USB_drive_%28Thunderbird%29

• http://kb.mozillazine.org/Move_a_profile_to_Portable_Thunderbird

• http://portableapps.com/apps/internet/thunderbird_portable

Thanks, that seems to solve it, but I also have this question:

Is there a difference in how Thunderbird (the normal, official version) installs if I do that on a USB drive vs a HDD? In the latter case (or both?), will it install in Windows registry or in "Documents and Settings" besides in the "Program Files"?

Thunderbird doesn't use the Windows registry. Its settings are stored in the profile, which in the case of the portable version, will be on your removable media.

Thank you very much! I prefer programs that doesn't use the registry nor "Documents and Settings".