I wish this was working for me. I'm a big fan of p2p technologies but despite watching messages scroll up my screen for the past few days, I'm still unable to participate. No apparent way to tell if things are healthy or not. I appear to be connected to a number of peers, I have my port forwarded, I'm running the downloaded windows binary, it should be a straight-shot as far as I can see but nope.
Am I really the only one having troubles or are others trying and just walking away? Is anyone driving this thing?
It seems that you are the only one with this specific problem. Since others can't reproduce it, it is harder to debug (and sounds like a configuration error, but you seem to know what to do to configure it properly and it still is not working). Maybe windows firewall? settings If you had a more recent python/twisted version from your linux distribution you could test that too to isolate if it is a windows configuration problem or somewhere else in the network (is your ISP filtering packets?)
I can share my experience: p2pool on a raspberry pi (raspbian wheezy), an ubuntu 12.10 laptop, and debian wheezy server all work with no problems with the default configuration. There are > 200 users using p2pool currently, and as far as I can see on the forums you're the first one to report the problem (which is why everyone is asking you to check configurations).
I hope you can get it working, perhaps stopping by #p2pool on freenode will get you some real-time feedback as opposed to long delay on forums.
EDIT:
Actually, could you try installing a more recent linux distribution in a VM on your slackware install? That should be easier than a whole machine upgrade and may show you if it is a windows or network problem.