I flashed my N800 with the latest firmware and I got this restart loop problem. Reflashing the machine would help to get rid of this restart thing? I have read the forums but i couldnt find how to reflash in windows vista.
any advise?

Try a search of the forum for LiveCD - basically, use a Linux LiveCD to boot your PC into Linux then flash the N800 using the Linux flasher. Other than that, are you sure the Windows flasher doesn't work with Vista? Have you tried enabling XP compatibility? How did you flash the N800 the first time?

Reflashing will probably get rid of the reboot loop, but it may also require enabling of the R&D flag and/or disabling of the lifeguard-reset.

Or you can try running the program in XP mode.

^ right, XP compatibility *might* do the trick.

thanks for your advise I'll try livecd as soon as i get back!
what are these R&D flag and/or disabling of the lifeguard-reset?

R&D and lifeguard-reset may be enabled and disabled, respectively, using the command line flasher.

Try running the flasher under Vista as an administrator --- as in, right-click the application and select "Run as administrator".

Older apps don't interface properly with UAC and are often denied requests outright instead of popping up the UAC cancel/allow box.