Hi calfrey and welcome to the forums
Below is a link to the main Lexmark site. In the left hand column, click 'Find Drivers and Downloads'. The default type of product, 'All-In-One Printers', is the correct category, and your printer model is on the 3rd page, so next to 'View Page:' click '3'. The X5495 model is the 3rd one on the top row.
For support, click on 'Get Support'.
For the driver, click on 'Download Driver'. Under 'Select Your Operating System' in the '--Select Windows--' dropdown box, click on 'Vista_x64' or 'Windows Vista' as appropriate. This will bring you to the actual download page. Download and save all available files. You should then be able to install the driver(s) by clicking on the downloaded files.
Lexmark - United States