CS3 and Canon G12

You need at least Adobe Camera Raw 6.3.  THat would require CS5.x Photoshop since the last ACR for CS3 is I believe 4.6.

So you will either have to upgrade (recommend hold out for CS5 in a couple of months) or use a DNG converter. 

DNG is free and you can download the 6.6 version.  It will work with all versions of PS.

Another approach would be to install Lightroom Beta 4 which will give you a working RAW conversion utility for a period.  (I guess the beta will time out when the full version is released.)  You could then pehaps purchase LR4 and cary on using CS3 and save some $$$

http://blogs.adobe.com/lightroomjournal/2012/01/lr4betanowavailable.html

And Adobe forum

http://forums.adobe.com/community/labs/lightroom4?view=discussions

[EDIT]  Taking this thread off at a minor tangent, (it does mention the G12 in the thread subject) DPReview put up some full res images from the G1X a few days ago, and its high ISO performance was outstanding for a compact.  I carry two 1D bodies when I a work events, and usually take a 1DsMK3 when travelling, and it wears you down carrying all that weight.  I used to have a G10 before my wife decided she should have it, so I am definitely in the market for the G1X when it comes out.

Try it up at ISO 3200

http://www.dpreview.com/previews/canong1x/page6.asp