I am about to go on vacation to Balboa Island, CA for three weeks. It
will be a working vacation. Since Comcast (my current high speed
internet access provider) doesn't offer service on the island and I
really don't want to be bothered with setting up DSL at the vacation
home we're renting, I was wondering if there were any temporary
solutions I might use short of setting up camp at a Starbucks. Are
there any PCMCIA cards I can insert into my laptop that would let me
access the web w/out wires? If so, which would you suggest? I have a
Dell Lattitude D800 laptop. My internet access needs are for IM,
email, and web browsing. High speed while nice is not a necessity.

Three types of solutions:
a) least inexpensive, least reliable -- camp out at free wi-fi locations
get a wi-fi 802.11b card. NetGear 802.11b Wireless PC Card is a decent one. 
Panera bread (Newport Beach, CA ? 1348 Bison Avenue)

b) inexpensive, but not too convenient
Use a tmobile hotspot. Purchase a wireless card and sign up for the
hotspot service. Monthly cost $6.00 for 60 minutes, $0.10 per
additional minute.

Nearest hotspot:
Starbucks, Balboa Island  (Café/Coffee Shop) Newport Beach  California
 T-Mobile USA

c) pricey, but more convenient and reliable
Use T-mobile's wireless internet. You'll need a specific card: Sierra
Wireless AirCard 750, $299.99. Service is $29.99 for unlimited usage.
 
I have previously used the sierra card and it is awesome (especially
back in 1997). The card also has GPS capabilities.

Forgot to mention ...
Tmobile hotspot sign up:
http://www.t-mobile.com/hotspot/services_plans.htm

Tmobile internet:
http://www.t-mobile.com/products/default.asp?class=data
Correction -- price on card is $249.99

I think that MercuryTX gave you a very good answer.  I have three comments to add:

Before leaving, find out if your company offers VPN for their
travelling employees.  If so, make sure you get your account and
client software set up so that you can get back into your corporate
e-mail.  T-Mobile's HotSpot service works very well with VPN services
(pptp, ipsec, ...).

If you already have a T-Mobile cell phone, T-Mobile's HotSpot service
is available as an add-on for a mere $20 per month (for unlimited
service) and they are in over 4,600 locations now.

It's possible to find 802.11 cards with external connectors such as
the Orinoco classic Gold card. 
http://www.proxim.com/products/wifi/client/goldpccard/  On the end of
the card, hidden behind a small plastic cover is a tiny microwave
connector.  With a small "pig tail", it's possible to connect an
external antenna such as a home made "cantenna", pringles can antenna
or with a commercial yagi from MaxRad.  If you are near enough or
within direct line of sight, this get-up will allow you to visit the
nearest Starbucks without leaving the farm.