1. Google maps API supports:
IE 7.0+ (Windows)
Firefox 3.0+ (Windows|Mac|Linux)
Safari 4+ (Mac|iPhone)
Chrome (Windows|Mac|Linux)
Android
Older or different systems may or may not work
2. You can download hi-res scans of topo maps from USGS. These are normal PDF files. They are not the new GeoPDF files.
Matt produced the hi-res topo tiles that Gmap4 displays by processing these PDF files.
A. Go here: http://nationalmap.gov/historical/
B. Then click on "USGS Store: Map Locator and Downloader" (might be down - check back later)
C. After you find the quad you want, click on file size to download