There are quite a few users that have succesfully run LabVIEW on XP embedded, however NI does not officially support such operating systems. Some components / toolkits may not function correctly if LabVIEW does indeed run on embedded systems.
Real Time targets are the prefered route, such as RT PXI controllers. Perhaps give your local field engineer a call.
As far as Windows CE is concerned, we have the LV PDA toolkit available that will run on pocketPC (aka windows CE). There is also support for PalmOS.
There are special considerations for PocketPC LV applications, as the engine on the PocketPC is a reduced set of that seen on a normal PC.
Have a look here for a little more info. (Either that or give NIUK a call)
LabVIEW PDA moduleRegards
Anthony Sims
Applications Engineer
National Instruments UK