What about .# files when using CVS?

We use CVS as version control system and sometimes some .# files appear in the Project view, e.g. .#Solution_GISMO.psf.1.484.2.2, and they get more and more over time.
As an example I currently have the following incarnations of the Solution_GISMO.psf file:

• Solution_GISMO.psf
• .#Solution_GISMO.psf.1.483
• .#Solution_GISMO.psf.1.484.2.2
• .#Solution_GISMO.psf.1.485

What are those files needed for? Are they needed at all? How can I get rid of them?

Thanks in advance,
Helge