Im not really the resident expert on Vista, but we have a few guides that will help you there, I'll get to those in a bit, but first thing to know is that running a smooth primary on Vista is really not any different (its more winmx specific tweaking needed) then any other person running Primary.
First step for you will be to forward ports in your router. Does the guide that Reef Posted in the other thread look like your model?
Second would be to make sure that WinMX is allowed in what ever firewall you decide to use, the Vista firewall will need ports added as well, but most other firewalls just need WinMX to be allowed.
Then there is the making sure your WinMX Settings > Incoming TCP & In/Out UDP settings match the port you set up in the router/firewalls.
WinMX uses TCP 6699 and UDP 6257 by default and those are fine. Again they will have
to be set up in the router in order to make a working primary connection.
Here are some tips for using WinMX with Vista, First one is to give WinMX folder administrative rights so that its allowed to operate properly and there is a guide here:http://forum.winmxworld.com/index.php/topic,4804.0.html
Its also a very good idea to move you're incoming folder from the default location for Vista.
Usually if you make a folder on the main drive (C drive) call it anything you like but dont use any real names, like mines named Share With The World, but hey just MyStuff will even work.
Then open WinMX Settings > File Transfers > Top right you'll see a incoming files folder path and a button to Change, select this and browse to your newly made folder (where you will also need to move any incompletes you wish to finish).
That helps deal with a couple Vista related problems with WinMX and should make things much easier for you.
If you have any specific questions after reading the guides Reef posted for you or the ones listed here for Vista just post back, I know its alot of info but we're here to help.