Yes, you can do this with a G7, using the included Canon software.
On the installation CD is Zoombrowser. From within Zoombrowser you can call the "Camera Window" and within that is "Remote Capture task". This controls all functions of the camera from the PC, and includes an intervalometer, which is what you need.
I've just tested it on my G7 and easily set it up to take 10 images at 10 sec intervals. You can set however many images (up to 999 I think) and whatever interval you like from 5 secs to 60 mins.
An alternative for tethered shooting is Breezebrowser (www.breezebrowser.com) which also will drive the G7, or many other Canon cameras.
BTW I highly recommend the G7, and I'm a 5D owner!
Have fun, let us see the results perhaps?
PS I used to have an S70, which had an in-built intervalometer for standalone interval shooting (never tried it but it might be of interest to you)