First of all, use google to find out how to use google. There are plenty of resources on the internet and on the google site itself.
Also, for something like files and filesizes etc, do a search for "search file sizes" etc, if it turns out it is something google doesn't handle. I know there are some ftp search engines that allow that.
I think google images allows you to pick generic sizes, and often you can do a search with say 800 600 b/c it is in the filename. NOt sure if you can do resolutions, probably.
There is a very popular handy book out referring to using google Google Hacks: 100 Industrial-Strength Tips & Tools Google Pocket Guide
That info should get you started.