How do I reinstall Ubuntu on a dual boot system
 

On my Ubuntu 10.04.1, the ethernet doesn't work for my dual boot (Windows Vista) machine. I can run Ubuntu 10.04.2 from a USB flash drive & would like to install it over the non working 10.04.1.
My Ubuntu is on my dev/sda6 partition (I think the swap is on sda7) but when I try to install on that partition I get a question about the root.

How do I install Ubuntu on that partition without messing up my Vista. (I did it wrong on my netbook & had to rebuild the whole computer). I think I can delete partitions, expand vista to take all the free space & then reinstall Ubuntu "side by side" but that seems like the hard way.

I don't know how to select the correct options to reinstall Ubuntu without changing the partitions.

The 10.04.2 installer is probably just saying that is has found an existing installation on sda6. Since you want to wipe out the non-working install, you just need to tell the installer to format the sda6 partition and install a new copy of Ubuntu.

In this case you would lose any documents or customizations/settings you made under Ubuntu 10.04.1, so make sure those are backed up before proceeding (if you need to keep them in the first place).

I selected "Specify partitions manually", clicked /dev/sda6, selected delete. Then the partition table shows "free space". When I select the free space & <forward> I get a message that says "NO ROOT FILE SYSTEM IS DEFINED" & then gos back to the partition table. I don't know how to procede.

For installation side by side with pre-existing windows & ubuntu:
Select side by sideThe os usually will detect ubuntu and ask if you want to install next to it.
In window you'll notice the size of partition will be split and show 2 ubuntu's.At that point select erase and use whole partition.

When I try side by side, it wants to split my windows partition, sda3, not my ubuntu partition on sda6. It wants to leave sda6 intact.

There's a bar at the bottom with an arrow click on arrow it'll show ubuntu.

You did it right. you deleted the /dev/sda6 partition. Now it should show some free space. 1.Select the free space or existing /dev/sda6.
2.Select create new partition or edit partition.
3.It should give you option to select partition size, partition format - ext3, ext4, swap. select ext4.
4. It will ask you mount point. select '/'. Thats called the root of filesystem - the error it gave you.
5. also select format partition option.
6. select done with partitioning and proceed.

Thanks, milindlokde, that worked.