When I get the new operating system installed, how do I export my address book from my existing Windows XP Outlook Express, can someone tell me please?
There should be an option in Outlook Express to export to something like "Business Card", "vCard" or "VCF". That will export the address book as a .VCF file, which is a standard (albeit ancient) format. Then your email package should have an option to import the same. (Unfortunately, I don't use Thunderbird, which is the Mint standard, so can't check this for myself).
BTW make sure you export all addresses, not just one!