I am thinking of buying a handsfree car kit due to the law about cell phones and driving. Is it hard to install one yourself? I have a porsche boxster.

Here is some info on installation: Parrot USA - Installation diagrams for hands free car systems

So, it depends. If you can get a harness kit, it makes life easier especially if you can get both ends.

As an example, see Parrot Kits and Quick Connect Harness Adapters

Click on "Why do I need a harness" as well.

For this mfr, it doesn't look like a harness is available.

If you've never taken a dash apart, it can be an undaunting experience. I've installed an AC unit from a box and an alarm system with home made door locks and a car stereo.