Motion has some keying abilities but if you need really robust keying effects you are going to need to use After Effects or Combustion (or Shake)
FCP has chroma and luma keys but they are not as good as the popular compositing tools versions. Some folks do very well with them but it takes time and patience inside of FCP.
Also depends on the material you are using - DV 4:1:1 is not as capable of using keys on as 4:2:2 Beta.