After a pleasant LiveCD experience, I went to install xubuntu this morning. When it came time to partition, I set up the following partitions:

-NTFS, ~65 GB (for existing Windows installation)
-ext3, ~12 GB
-swap, ~2GB
-FAT32, ~900MB (for sharing files between Windows and Xubuntu)

When I hit "next", the partitioner said it was starting to set things up. It looked like this would take a while so I went to take a shower. When I got back, it had a list of partitions:

-NTFS, 75GB
-blank, 0k
-blank, 0k

Uh-oh. Of course, it won't let me set the 0k partitions to be root or swap, because they're too small. Went to the file manager, and it reports that I have one 75GB unformatted partition, and that there are three more of 0k. Also, the partitioner at this point refused to quit (e.g. Quit button brings up "do you want to quit" dialog, but saying Quit on that does nothing), so I just shut down Xubuntu.

Yeah, you know where this is going. Windows doesn't boot - just a flashing cursor when it gets to C in the boot sequence.

What should be my first steps to fix Windows? I want to get this right and not do more damage. fdisk /mbr? fixmbr? fixboot? Is there a linux utility (I can still boot from LiveCD)?

I would recommend using SysInternals or BartPE CD 1st to see if there is still any need to fixmbr anything.........
But if you just boot with your win cd, you'll have to get to the repair state using
the recovery console. There you have to perform the following commands.
1. fixmbr so that the MBR is cleared out and no GRUB or whatever is present there anymore
2. fixboot so that the needed windows files are copied back
3. bootcfg /rebuild in order to auto recreate your Boot.ini
Then I strongly suggest to use Partition Magic or Acronis Partition Expert in order to "smaller" your win NTFS partition. Leave space behind free and unpartitioned.
Then start the xubuntu install again.

regards

Sweet. Thanks oddcheck, your 1-2-3 steps did the trick.

Regarding the reinstall - I'd rather not shell out the money for one of the commercial products. But tell me, might it help if I were to use the "alternate" install CD iso for xubuntu? I understand that's the classic text-based installer/paritioner, so if the underlying paritioning code is different maybe I'd have more luck there.

The linux-ntfs project has some awesome tools. Do not pay for NTFS tools.
They have a resizer (no defrag required), and a ntfsclone to create a compressed backup that can be used if a restore is required.

Yes, I use the resizer regularly - bloody magic.
I prefer the CLI tools, but the project recommends the gparted liveCD (small download) if you want a GUI.
Go look here.

okay try the text mode thing but regarding this expensive products there is also freeware around there in the I-Net.
And BartPE is a free PRE-Windows Enviroment also a good job and some good tools has got the ultimateboot-cd.
How ever I hope it will work and I also hope you will learn an use Fedora sometime somewhere..