Im trying to install the driver for an adapter for serial to USB conection, (BELKIN FSU109), my cotmputer works with the Windows XP Media Center Edition, when I try to install the driver, it fails the installation process due to the "digital firm" is not compatible with this version of windows.

The website of the manufacturer doesnt have any upgrades.

What can I do to solve this?

not knowing what type of PC you have, but assuming it is an older one, if you need to go from serial to USB, I'd suggest you buy a PCI-card with USB2.0 ports on it, amongst others also available from Belkin (5-port card).

A better product seems to be the OrangeUSB 2.0 PCI Card
Price: $50 street
Company info: 714-779-2772, www.orangemicro.com

See below for opinions:
http://www.pcmag.com/article2/0,4149,847802,00.asp