If you want to add a costum xsl to your sharepoint list view you can do this by duplicate the existing ones (if they fit to your aims) and add them in SPD 2010 to your list. Act like that:
- to to /_layouts/xsl/ and locate the xsl you want to edit (e.g. main.xsl or blog.xsl)
- add connection to the new view (e.g. vwstyles.xsl), safe under new name
- duplicate root xsl-view, edit the views
- go to the desired list, open up in SPD 2010
- Go to the list, open up the settings and locate the xsllink settings
- link to your new xsl, that`s it;)