Short answer - no, you need wireless infrastructure (a router or access point)
Long answer - if you can make your laptop route between the ethernet and wireless interfaces then it may be achievable.

I managed to connect my chumby via an ad-hoc connection, so it is definitely possible.

But I had to set the connection-settings myself in the debugchumby-file, because the controlpanel didn't accept my settings.

Sure!

I put the following lines in my debugchumby-file:

iwconfig rausb0 mode Ad-Hoc essid mywifi key off
ifconfig rausb0 192.168.2.2 netmask 255.255.255.0 broadcast 192.168.2.255

On my PC I set up the wifi to use "mywifi" as essid, gave my PC the IP 192.168.2.1 and enabled the "internet connection sharing" on my lan-connection.

If your laptop is capable of serving a wireless network in infrastructure mode (i.e. acting like an access point), you can configure chumby to route to the internet through your laptop.  I've posted instructions on how to configure your chumby to connect wirelessly through a MAC laptop here -
http://wiki.chumby.com/mediawiki/index. … MAC_laptop

Ofcourse, you could also order a Fonera! and be even more open!
(I just ordered one for about 12€, including a very strong antenna!)

http://www.fon.com/en/

The La Fonera protects your connection with two secured WiFi signals:
One encrypted WiFi signal that is only for your own private use
A second one that requires authentication and is for all other registered Foneros
PRIVATE...MYPLACE

With your private FON signal, only you can access your computer and files. The encrypted signal is yours alone and YOU ARE THE ONLY ONE who has its key!
PUBLIC...FON_AP

With the public FON signal, only registered Foneros can access the FON Community but cannot access your private network. ONLY FONEROS have keys that connect to this signal! If someone doesn't play by the rules, FON will be able to identify them at the public FON signal.

Remember! FON is a Community of registered users. All Foneros are required to enter their username and password to access the FON Community. NO KEYS, NO FON. The security and protection of all Foneros is safeguarded. The La Fonera updates reinforce your connection's security! Keep your La Fonera online...it updates automatically!