Yes TomTom is available for P1i and you should use the UIQ(3) version of the program. Remember that even though both (Nokia) S60v3 and UIQ3 are based on Symbian 9.1 the UI code is different so always use UIQ3 version applications on your P1i (older UIQ wont work either).
I think you can get it from Tomtom.com directly. Although it says it supports only SE w950i it will work on your P1i. Just dont buy the program on the memory card since they are Micro SD and not M2 which you would require.