I recently acquired a new PC with Windows Vista on a 320 GB drive. My goal is to install Windows XP and Ubuntu Linux, but also keep Vista. I haven't powered it up yet, but I assume that the C: drive is taking up almost all 320 GB. Here is my plan of action:

1. Use Partition Magic to shrink the Vista partition to 100 GB, leaving 220 GB free.
2. Install Windows XP into a new 100 GB partition, leaving 120 GB free.
3. At this point, when the PC boots, it will give me the option to choose Vista or XP, correct? Will BOOT.ini be automatically updated when I install XP?
4. I will then install Ubuntu, and its Grub should overwrite Windows' boot.ini, and give me the choice to boot to Ubuntu, Vista, or XP.

Am I missing anything? THANK you.I'm not sure if you can have more than three partitions on a hard drive. (Anyone know for sure?)
You're going to need two partitions for linux, unless you're planning on not having a swap. (bad idea)
My recommendation: Get another hard drive.
Also, linux will not do anything with the boot.ini file. It writes a boot loader to the mbr. So when you START the computer, you'll get grub and if you select windows, you'll get the windows boot options. You might be able to get rid of the boot.ini file if you just want to use grub, though. Don't take my word for it though.
I think vista might be able to shrink partitions by itself. I know the 2008 server beta can. Right-click on my computer and click manage, then go to disk management. Play around with that a LITTLE and find out.
You can have 5 partitions on a HD. The only limit is that you can only have 4 primary partitions, which should be enough for your plan. Your plan sounds fine michaewlewis. Grub should detect your windows installations so you should be able to boot all your OS from grub.Actually if it were my computer, I would have a separate hard drive for each os and split each one into at least two partitions. One for the os, and one for files (and one for swap in linux). That way if I ever need to reformat and reinstall the os, I could do it without losing any data. Also, if one of the drives fails, I wouldn't have to install all of them again.