you can use asus rest. tool, or windows tftp, no need to download anything.
On winXP you go to:
- start, run
- enter "cmd" to get a dos-windows
- use my description or any other

I guess (not sure) tftp is a part of windows.

dont worry, do it step by step.
As I can see, your native language is german. If you want, I can guide you in the german forum.
have a nice weekend.....