What is it?

fxssvc.exe is a file associated with the microsoft FAX application

what does it do?

Fax provides you with complete fax facilities from your computer. You can configure fax settings, send and receive faxes, track and monitor fax activity, and access archived faxes.

More info:

[url=http://www.microsoft.com/windowsxp/home/using/productdoc/en/default.asp?url=/windowsxp/home/using/productdoc/en/app_faxclient.asp]microsoft.com[/url]