Brian,
By all means, you can post your Pireps manually on the website (Goto - Pilots > PIREP) if you are using Windows Vista.
If you are running FSX under Windows XP then it should still work although you will need to download Version 4 of Pete Dowsons FSUIPC which is designed for FSX.
At the moment, we are relying on pilots to experiment with the system and let us know what they find, so feel free to try it out. Unfortuantely, we can offer little support at this time as the Dev team have higher priorities. I am one of the MT who is attempting to run FSX, so feel free to email me with questions or problems, or indeed post any findings here as I am sure there are a few other Pilots who have made the switch to FSX who might be able to share experiences.
Good luck.