[ubuntu] How to get a clean re-install?

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http://ubuntuforums.org – Hello, all. I'm just starting out with Ubuntu (LTS, installed in dual-boot with Windows XP Prof using wubi). I did a real bad thing in the command line which appeared to start mass-deleting loads of packages. I stopped that process, after which the software center stopped working. All my working data is in Dropbox, and I had a bunch of software installed I didn't really need so figured I would be better off nuking it all and restarting. I booted to Windows, uninstalled with wubi, then re-installed. On booting into Ubuntu, it acted as if the old install wasn't purged - my userid and pa (Hardware)