The file you need to generate for the TomTom is called "contacts.txt" (it's in a folder called "contacts") and is also a simple text file.
If you have already imported a phonebook from a phone, then you can easily open the text file in Notepad to see the layout, which is basically Name, Number, Type, like this:
"Fred Bloggs","01234567","WORK"
"John Doe","+441914987654","HOME"
"My Mum","09876544321","CELL"
I presume you can export the contacts from Outlook as a text file somehow?
Once you have that, you could use whatever program you like(word, excel etc) to put the formatting ( all the commas and quotation marks) in the right places)
I have an excel template which might help
here