The GSiteCrawler generates several files - which one do I upload for Google Sitemaps?
By default, the GSiteCrawler will generate three files:
The actual Google Sitemap XML file is the "sitemap.xml". This is the file that contains your URLs and the data which Google Sitemaps needs to crawl and index your site better. The "sitemap.xml.gz" is just a compressed version of the same file. If your site is fairly large or if you need to make certain that Google uses minimal server resources (bandwidth, etc.) then you can use the GZ-compressed version of the file. Other than the file size, they are technically not different.
The "gss.xsl" is a XML style sheet file which is used to display the XML sitemap file in a browser. You do not need this file, but it might be useful if you wish to view the sitemap file in your browser. Google does not use this file.
If your site is larger than 40'000 URLs then the GSiteCrawler will automatically generate a sitemap file per 40'000 URLs (the files are numbered; of course the compressed versions as well). In this case, the GSiteCrawler will also generate a "Sitemap Index" file with links to the compressed sitemap files. If several sitemap files are required, then you should upload the compressed versions of the sitemap files along with the Sitemap Index file. You will only need to submit the URL of the Sitemap Index file to Google - it will find the compressed sitemap files from the links in the index file. Google officially has a limit at 49'999 URLs; 40'000 is the default used by the GSiteCrawler, but you can change this value yourself in the "Global Options" window.