Hello,
I have Inkscape 0.48.4 installed. I can work normally with Inkscape: filters, blur and so on, While I see alright in my screen, but not in the print preview or when I print it on the paper. Filtres and blurs appear always fuzzy on the print. Why is this? Could somebody help me please?

Not all colours from screen are available on paper. For starters.
Either consult some color chart for printing/printers in order to get closer to desired result or perhaps provide a preview?

Even if you use "printable" colours, it could happen that some gradients or colours overlapings are not as desired when printed on paper. In these cases, chosing "right" type of paper or type of colours, or even method of printing could solve the thing.

In short, your disappointment is not related to Inkscape only but to the inevitable limitations of printing. ( till we see the preview ,)

Thankyou for your answer, yes is true that colors change on the paper. But I think must be another reason for the problem I have. Because for example lines and gradients appear clear. but not the most of the filtres and blurs... They apear like pixelated in a strange maner.
And moreover, that is not only on the real print, but in the print preview too.

The problem has been finally solved by reinstalling Inkscape 0.91. Now I have the curiosity to know what was happening, may be a mistake of the program...
Thanyou.

Well, if it works - job done! ,)