Like Ian said, it seems that your previous web master simply did the initial footwork, then loaded the final page in DW and transferred the code over solely to HTML-structured code.
The FTP access is going to be your SERVER login and password (generally the admin account, say "Username: admin & PW: password". DW is alright to use, though the setup is a bit of a PITA...
Go to the 'Site' menu (up top between 'Commands' and 'Window' and click on 'New Site'. Name your site and put in the URL of it > 'Yes' or 'No', depending on your site's 'technology' > Skip the radio button and put in the directory where yur files are stored ON YOUR COMPUTER (this gives the FPT program a place to 'PUT' files from > Dropdown - FTP, address yould be ftp://YourSiteHere.com - type in the directory you have your DNN files stored (probably 'dotnetnuke') - put in your server login and PW (check 'Save so you don't have to keep inputting your Login and PW everytime) - Click 'Test Connection' and it will verify all of your stuff, spitting out an error if there is one.
*MY* recommendation is to use FireFTP - a nifty plug-in for Firefox. It's REALLY easy to use. Just set up the account (Your server's name and ftp://YourSiteHere.xxx, supply the login and password and it will do the rest... It'll even keep your folders (local and remote) in sync.
Basically, the setup is ROUGHLY the same, though not so many steps.