You won`t be able to upgrade if there will be no official upgrade for the device.
There isn`t just one Version of a operating system for ppcs like it is for desktop.
If you want to upgrade your desktop you can go to a shop and buy a copy of XP or Linux. For PPCs there need to be a Version of the OS which is "designed" for your device hardware. If there is no version from the vendor you can`t use another.
If you want to develop applications for PPC with .NET 2.0 just go to MS Website and download the 2.0 Compact Framework. At least the framework ist device independent and you can install it on your X30.
You won`t be able to develop apps for WM5 and test them on a real device if you don`t buy a WM5 device or use the Emulator.