If I use Bootcamp, Can I later repartition with..

VM Fusion or Parallels or is it too late? Know what i mean?

You don't need to repartition your drive for using it with Parallels or Fusion. They both create a sparse image within the OS X partition (or if you want to specify somewhere else, that's also fine).

Thanks, ..but what if I partition now for Bootcamp? can I

"unpartition" later and get the space back?

Yes...if you want to, you can migrate all of the data from your Windows partition into Parallels or Fusion (I think Parallels calls it migrator or something). Make sure you tell it you want it to setup and use a NEW virtual machine, you don't want it to start the virtual machine off of the BootCamp partition every time. Once you have it set up this way, you can run the BootCamp assistant again and tell it to rejoin your Mac OS X and Windows partitions into one and get all of your space back. From then on you'll use the "Virtual" partition that Parallels or Fusion stores in your Home folder to boot the virtual machine.