Installing Ubuntu Over Fedora

[waqawaqa]

I have a system with dual boot, Windows 7 and Fedora 12, the GRUB is by Fedora 12, As I forgot the password of Fedora, and I could see that My fedora box was very slow.. I want to overwrite the Fedora by Ubuntu, is it possible? if yes kindly suggest the trick.

[plasmafusion]

yes. very possible. just install ubuntu like you did fedora and overwrite the existing linux partitions...leaving your windows partitions intact. grub will be updated and will offer ubuntu and windows boot options.