Do you still have an operating system with Thunderbird installed on your old hard drive?
If so, download this prog click here install it, make a backup of your settings with it.Then transfer your back up to a floppy disc, cd,or whatever.
Reconnect your new hard drive install "Thunderbird",and "MozBackup"
Then restore your stored backup to you're new PC.
Thats the prog I use for my Thunderbird backups,and I find it the easiest way.
Your Thunderbird profile is stored in
C:\Documents and Settings\User name\Application Data\Thunderbird,making sure your folder options are set to "show all files" someone else may be able to tell you how to do it that way,I've always just used Mozbackup.