The final sollution:

So the HP Support send me the original CD Pack - that was their sollution,
but I solve the problem myself.

1. I reinstalled the WinXP Pro TabletPC edition
2. I nstalled the WinXP Pro English and Hungarian MUI
(I got the Hungarian MUI from my turkish firend - because the WinXP Pro MUI
CD4 contains the hungarian language - and turkish, polish etc.)
3. I installed SP2
4. ...than I installed the MUI package for TabletPC 2005 from MS

....and it works - I have a fully operable hungerian gui! Even the TIP is
hungarian!

Now the only thing I need is the hungarian handwriting and speech
recognition pack - which does not exist yet... ;)

I think it will work with every rare language - you just have to get and
install the MUI for your language before installing SP2.

Unfortunately HP is packing only the chinese, french, german, japanese,
korean, tajvanese, portugese, spanish brazil-portugese, danish, dutch,
finnish, italian, norwegian and swedish MUI (WinXP Pro MUI CD1, CD2 and CD3)
in the box, but there is several other MUI CD on the world, but unfortunately
you can't buy it any way... So lets bother the TabletPC manufacturers to pack
the local MUI CD in the box in your country - because they have the licens
for it!!!