mbox is a text format, so you could open it in notepad or whatever (though it'll be kind of awkward, you can at least read it--it's okay if you just need to quickly look up a couple of things).
Thunderbird you can install the free importexporttools plugin and import them.
http://kb.mozillazine.org/Importing_folders
There are various mbox to PST converters (for use with Outlook) but I've not used them.