Ok, here is how I sorted anything out since apparently the software available for Windows 7 has some kind of bug somewhere:
1. Download the Xerox WorkCentre 3550 PcFax software from here: http://www.office.xerox.com/multifunction-printer/multifunction-over-30ppm/workcentre-3550/enus.html#yscroll_300 (browse here and there and you should be able to find it)
2. Install it trying to locate your MFP 3300 by IP - this will give you some errors (s.a. printer is not compatible... printer unavailable... printer's gone fishing... blah blah blah) just ignore them and install the program.
3. Open the document you want to send by fax and do anything as usual (File, print...) and select Xerox MFP PC Fax. Hit OK.
4. A window pops up and at the very top of it you should find "Model:" and "Ip address or name:" anything here should be blank click on "Change" botton on the right.
5. Another window pops up (I didn't tell you it was easy but it won't take long, promised) select "Network" and manually enter the printer IP Address. Hit OK. Needless to say that now you should see Model: Xerox 3300 MFP and its IP address.
6. Now select all the fax numbers you wish from either the Windows Contacts or Outlook (Yahooo! You do not have to set up that crappy "Pc Fax Settings" stuff any longer) click in the arrow in the middle and once you've selected anybody click on "Send".
Xerox, please, correct the bug or issue some kind of software that works with Windows 7 and 8 or at least do a step-by-step troubleshooting tutorial out of this post.
So, mission accomplished and the problem is sorted out somehow.