There are directions for using pulse-jack and a lot of other stuff here
The pulse-jack info is near the bottom of the OP in the Ubuntu Studio section.
If jack is running and using the HDSP then it is unavailable to pulseaudio and so will not show up. It should show up if jack is closed and some other app has not already grabbed it while pulse was sleeping
If you are happy with your setup I can not really recomend you changing it and pulse in Jaunty is not really working as it should so I have not fooled around too much with the pulse-jack stuff there but others have and it seems to work well for them.
But, if you want to add a little functionality like applications playing through pulse being available to connect through jack then the pulse-jack modules are pretty easy to get working as you will see in the link above. What it does is creat a jack-sink and jack-source in pulseaudio and create pulse input and output clients in jack. The jack and pulse devs have been talking with each other lately so hopefully we can get some more from this in future versions. There are a few things you need to be careful with but they are explained.
Sometimes I use the pulse-jack sink to add effects to streams playing in Amarok, or record you tube with ardour, or play along, things like that and to get record-my-desktop working. It can all be done on the fly without having to restart jack or any of the apps to change devices so it is very handy in that regard. The alsa/pulse apps stay in pulseaudio and the jack apps stay with jack and the pulse-jack sink lets you connect them without losing anything from either one.
Pulseaudio is going through some big changes lately. Pulse0.9.15 has a much better volume control with a lot of added functionality and they expect to add even more with future versions along with playing better with jack. They have not jumped to version 1.0 so I suspect the devs feel pulseaudio is still somewhat incomplete.
But, things are looking up soundwise, FFADO is working better, Jack2.0 is very close. When jack gets back into the /main repo a lot of these issues will go away.
A little history so maybe you can understand why all of a sudden so many distros moved to pulseaudio and why everything has become so confusing. The alsa drivers have been moved into the kernel. Due to kernel security concerns this move brought about a big change in the way the alsa drivers should be communicated with. It is no longer acceptable for applications to be able to directly manipulate the drivers since they are in user space and the drivers are now in the kernel. Since the ALSA sound server (not the drivers) architecture (esound, demix, et al) was such a mess and so many changes were needed to conform to this new paradigm, it was easier to just abandon it and institute a new sound server that would sit between the drivers and the applications and prevent user applications from intruding on the kernel space. Pulseaudio, unready as it was, was about the only thing that fit the bill and so was adopted by ubuntu and fedora and suse and mandriva etc.
Meanwhile, KDE, as they are wont to do, started developing their own new sound server, Phonon, which has replaced aRTS in KDE4 and is very similar to pulseaudio but is still very much a work in progress.
And OSS has jumped back in the game but nobody is taking that too seriously since their previous abandonment of the Open Source community generated a lot of resentment and mistrust. (The devs took OSS private and started charging for it.)
Meanwhile jack stands apart from all of this and continues on its dedicated but limited mission. To provide a low latency controller for professional quality sound production. Jack will never be a sound server but the jack devs are working to get jack better integrated into the sound server scheme without compromising the mission.
Soo, the linux sound scheme is in what can be charitably called a brief period of flux. Hopefully it will all settle out in another year or 2 and these new sound servers will have their act together. Meanwhile you can still fall back to the old ALSA server stuff but I think much of the server side API will become deprecated over the next few years due to security concerns.
That was probably way more than anyone needs to know.