Q: Is it ok to cast a string to a pchar?
A: Yes. Delphi long strings (the default string type in 32-bit Delphi) are designed specifically to allow typecasting to PChar.
The following code is valid (with Delphi 2/3/4):
procedure p;
var
s : string;
begin
s := 'Hello world';
// set the current window's caption
SetWindowText (GetActiveWindow, PChar(s));
end;