Thunderbird uses the mbox file format (even though it doesnt add that file extention)
To get these emails into Outlook 2007 you first need to convert them to .eml files and then import to Windows Mail and then from Windows Mail import to Outlook .
Thunderbird to mbox
Open in windows explorer the location of your thunderbird data files (probably c:documents and settingsuserapplication datathunderbirdprofileshdjsd.defaultMaillocal folders)
Rename the file called INBOX to INBOX.mbox
You may want to copy the files first just incase something goes bad and then do the same for all the other folders you want (sent, trash etc)
.mbox to .eml
Go to http://www.broobles.com/imapsize/download.php and get IMAPSize.
After its installed under tools is mbox2eml, select the mbox files and it will extract all the .eml files
.eml to Microsoft Mail
Open the folder you extracted all the .eml files to and then open Microsoft Mail
You should now be able to select all the eml files in Windows Explorer and drop and drag them into the approperate folder in Microsoft Mail.
Microsoft Mail to Microsoft Outlook 2007
Close Microsoft Mail and Open Outlook
Click Tools and Import
Select “Import from another program of file”
Select “Outlook Express 4.x, 5.x, 6.x or Windows Mail”