What he said.
Only even better than "semi"-possible.
I've read reports that if you use pretty much just the most basic components, porting from Delphi 5 to Kylix was just a few code corrections.
Between Delphi 6 and Kylix, it should be only the names of a few units in the uses clause.
In both cases, a couple of ifdefs per unit file should make your code cross-platform.
Christian R. Conrad
The Man Who Knows Fucking Everything