well you can check out opensimpad.org and decide if you want to test Linux or if you want to upgrade to Windows ce 4.1.
The legality of the Windows ce 4.1 Image is not clear. Microsoft didn't answer until now. But I think the possibility that it is not legal is higher than that it is legal.
Than you can follow the guides on the Linux or Windows pages.
If you have troube to understand the guide - we can try to improve it - so others will profit as well. Just wirte about your problems with the guide here and I or you will upgrade the wiki (opensimpad.org) than.
Upgrading to WinCE 4.1 is less dangours than upgrading to Linux. Because for using Linux you need to change the bootloader. In some bad cases it could be that this will fail (e.g. powerloss while flashing). Than a JTAG may will help to bring it back to life (see mods jtag).
If you want to go back from Linux to WinCE later you will also need to change the bootloader again.
I prefere Linux but it is your choice
I will also offer a upgrade (flash) service - if you want just drop me a line at contribute | opensimpad | org
Payment is not neccesary (except the porto) just give me what you want after getting the SIMpad back.
But I will help you also here on this forum