For the last few months I have been diligently searching for an
enjoyable activity to occupy my free time. I don't have much interest
in my old hobbies and goals. Can you help give me some ideas?

The activity should match these criteria:

* Matches my personality (http://www.personalitypage.com/INTJ_car.html)
* Does not involve heavy computer use (use computers at work and my
hands are a bit sensitive)
* Provides a lifetime (or more) of challenge
* Does not require use of a car

Here are things I still enjoy but don't do as intensely as I used to
and don't feel as passionate about:

* Movies, quality TV (want to build my own home theater some day, but
it takes lots of cash)
* Hard science fiction and detective/police procedural novels
* Dating/women
* Building websites
* Talking philosophy (used to help run the philosophy club at university)

Some things I've enjoyed in the past:

* Playing Chess, Go board games (chess club in high school)
* Strategy computer games (e.g. Civilization 2) and other types
* Watching bizarre/funny videos online (made my own comic strip earlier this year)
* Bargain-hunting computer hardware online
* Meditation, Buddhism (attended a Zen center for a few months last year)
* Running a debate chatroom on IRC
* Political writing/news/activism (wrote for a student paper at the university)
* Digital photography

Please let me know why the activity/activities in question you come up
with would be a good match for me.

Thank you!

Sounds like all your interests to date involve being inside and
sitting around. If you are near a body of water with a yacht club,
wander down there on a weekend and offer yourself as a crew on ANY
yacht. You will surely get a place. The skipper will teach you
anything you need to know. Get seasick and get over it. Much as I like
computers AND religion, the ultimate is taking a little twenty footer
down the coast into the teeth of a 30 knot sea breeze and arriving at
your destination...BY YOUR OWN EFFORTS. This thinking can be applied
to just about any outdoor activity. Try it and see!.

You might consider quilting.
There are all different levels and styles of quilts.
From your comments it appears that you enjoy a mental challenge and
actually quiilting involves creating puzzel pieces and then putting
the puzzel together.

Woodworking, cabinet & furniture making is also very analytical,
precise and yet creative. Might consider building doll houses for
children, either in your family or to give away. There is a lot of
information on mineatures, and there are ideas to building and
furnishing doll houses at low cost.

Is there one area of your political interests that you could turn into action? 

What climate do you live in?

I'm a INTP so some of these might not be quite right for you but some
should be close.  Take lessons on a musical instrument.  Learn to play
Jazz.  Take a course at the local college.  Read ~30min of something
new non fiction every night.  Try to get it completely out of your
area of expertise.  Browse your local library non fiction, pick and
read a book every 6 ft of shelf space starting at 000.  Pick up a new
sport you will probably find one that is challenging (try skiing if
you live in a warm climate, and diving if you are in the north).  Read
the paper and find clubs in your area.  These are activities that
people (even some INT?s) enjoy enough to get together in groups.

WELL I REALLY THINK YOU WOULD LOVE THIS ACTIVITY GO BUY A FISH TANK
AND SETUP A SALT WATER FISH TANK VERY TIME CONSUMING GREAT TO WATCH
AND WILL NEVER STOP LEARNING NEW THINGS ABOUT IT.VERRY FUN COOL
RELAXING AND GREAT HOBBY. OR YOU CAN LEARN HOW TO DO BONSAI TREES
THOSE ARE PRETTY COOL AND FUN TOO.

Pugwash, what an interesting new insight on you! :)

Purify your mind,
If your user name suggests a continuing interest in philosophy, you
could host a forum/discussion group on the subject  (face-to-face, not
online):  weekly meetings discussing one aspect based on a reading of
an assigned  - not too long - original text.  In rotation, one person
could be better prepared and lead the discussion.  If there is a
college nearby, maybe a professional could speak.
The discussions might not be very deep, but a lot of people have a
latent interest in philosophical questions  - just who the Names are
and their basic ideas -  and might welcome the opportunity to be
induced into doing a little reading.
The Greeks are very readable, Plato's discourses, delightful.  Then
there are Hobbes and Locke on society and politics, and, and, and ...

I found a group like this very interesting, but each session started
with 1 + hour lecture by good people, but after dinner, that puts me
to sleep.

I also like Roxrox's suggestion of woodworking, the fun of designing
something in detail, down to the steps of contruction, and then seeing
if one is capable of actually doing it.  (I've got a beaut project all
worked out, material collected, but cold feet about whether I can do
the fine work properly  :-/ )

Myoarin

sounds like you're the perfect candidate for 
Texas Hold'em Poker.
it's stategic, easy to learn, but very difficult
to master. You don't need to be in great
physical shape but your mind needs to be sharp.
If you play well, you could make enough
money to pay for your home theater.
Especially if you play no-limit hold'em
where you can lose all your chips
at any moment. or double up.
Check out the WSOP on ESPN or
the WPT on the travel channel to see
if it might interest you.
Many players use philosophy to develop
a game plan and many good players are
brilliant mathematicians.
The high level players play a very
complicated game that most people
don't grasp.
You can play online at a variety of
web sites for free - in fact don't play
for real money in the beginning.
Partypoker.net or UltimateBet.net
or FullTiltPoker.net are some good sites.
I think there are over 6 million people
now playing poker in the US.
There's a reason for its popularity.
It's like chess but you don't have to know
your opponents move 6 moves from now.
And because it's poker, there is some
luck to it which makes playing even
more challenging.
just a thought....