Maps series 8 work correctly on Wince 4.2 TT7.
I suppose you are using TT 7.45 or TT 7.91. Both of them works.
But you have to look for a compatible map for PNA/PDA.
All maps use to work correctly on TOMTOM devices, but not all maps do it on PDA/PNA.
I have 8.55 maps running o.k.