There should be a page for your product on this site (Sony UK) with download links.
If you are a computer geek you could also try to find XP stuff in the VAIO downgrade directories on the FTP server: ftp://ftp.vaio-link.com/pub/VAIO/DOWNGRADE/ or ftp://ftp.vaio-link.com/pub/OS/XPDOWNGRADE/ (do not try to install random software from this FTP server, download only if you are 100% sure that it is precisely what you want).
Added later: I'm far from sure that you have a USB driver problem. Windows is supposed to install drivers, you can check what it finds in the device manager. Click on "show hidden devices" to get a complete picture. Click on "update driver" if you don't use that option in WU (windows update). Determine the manufacturer of your USB stuff (e.g., Intel), visit their site to find XP drivers if Windows fails (it should not fail for XP and anything Sony uses in their laptops, unless it's a very new USB-3 device). You could also ask in the Windows XP forum on the answers.microsoft.com site - I vaguely recall a trick to uninstall everything USB, reboot, and let Windows reinstall what it needs.
Maybe you have a hardware problem, no new driver can fix a faulty USB connector.
