Depends what you mean .. do you mean something similar to minimenu? or more like xfce?
We have a config file to set a 'desktop environment', which is how users can switch between minimenu and xfce (or others); you could just adds your to the end and good to go, really; your pnd would be an installer to add/remove your entry there, and install into NAND (you wouldnt' w2ant a launcher in pnd or on removable media, for obvious reasons
So, that takes care of users changing menus, and how you get launched.
As to operations and livecycle, thats up to you..
Minimenu's lifecycle is to come up, and then when it launches a pnd, it _exits_ and launches the pnd, to minimize memory footprint (almost none. Like 5K footprint
xfce is more traditional in the Window Manager style, where it stays live always, and lets you multyitask, with handy app flipping and window management and so forth.
If you make a new menu, do you mean to replace somethig nlike minimenu, or augment it.. somethign that comes up while another desktop environment is in control? (like a pause screen)?
If you're replacing one, then chances are you'd be operating like minimenu, since writing a full window manager is a Lot of work

Now that said, if you wanted to leverge part of minimenu (like the mmwrapper that does the launching of pnds and launchign of mmenu UI) you could, or roll your own.
Anyway, fill me in with details and I can guide you in the right direction
jeff
As to how to capture keys.. we have a daemon that watches for various things to happen, so it can react; like when the screen lid closes, it fires off a script to turn off the display; see the conf file at /etc/pandora/eventmap if memory serves.
The pandora button launches a script, which in turn checks if its 'xfce or somethign else'; for xfce it pops up the xfce menu, for everything else it attempts an app kill, on the assumption this will let the suer preferred menu come back up (ie: minimenu.)
IF you wanted one of those behavious, easy.. or if you wanted another behaviour, we could script it in.