I managed to make boot from SD. But now I have no idea how to transfer files from my PC (WinXP) over USB.
Any advices?

How about installing OpenSSH and using an sftp client like WinSCP? Transfer rates are a little slower, but there's a lot less work involved.

yes, I think about it, but PC and n800 don't see each other

My experience with sftp is Linux only, but here things are some things to check:

- make sure that openssh is installed on the tablet
- in my experience sometimes the sshd daemon on the tablet stops
working. start it with "sudo gainroot" and then "/usr/sbin/sshd &"
- check the ip address on the tablet using "ifconfig" or let your router give the tablet a fixed ip address on your local network.
- change the root password on the tablet in case you don't remember what you used when installing openssh on the tablet
- try if you can log in using ssh instead of sftp
- try connecting a few times. Sometimes it works after two tries

grrr.... have you ever noticed that I asked about "transfer files over WLAN/Bluetooth/GSM" ? no? may be because I don't ask about it?

Sorry I misread your question. No need for the attitude though.

Not sure if you still need help about this but provided you have OS2008 installed and you have enough battery charge, you just need to power on tablet and then connect it to your PC.

Your PC OS should automatically detect it. It worked for me on Linux and Windows is usually much better at auto-detecting stuff.

Here's a link to a tutorial that covers it.

If you boot from SD, you can't access that card over USB.