VueScan is a terrific piece of software that supports hundreds of scanners. It appears to support the Scanpartner 300C:

http://www.hamrick.com/vuescan/vuescan.htm#fujitsu

You could try Googling for Fujitsu's own drivers, and I suppose it's possible if you have Photoshop that its built-in TWAIN driver might work. But as a fallback, VueScan will definitely work - and it's better than many manufacturers' own drivers.

M