>>One thing to be careful of is reducing the size of an existing partition. Suppose you have an existing machine with a 160GB hard drive, with the whole drive partitioned as a single volume (C:).
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>>Only 20GB or so may actually be in use on Vista, so you say, OK, I'll repartition so I have an 80GB Vista64 volume and free up 80GB for something else. This means reducing the Vista volume from 160GB down to 80GB.
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>>A lot of OSs don't like having their volume sizes reduced, especially the system volume. It basically means defragging so there are (hopefully) no files at the end of the volume, then reducing the volume size. In some cases defragging may not be able to move files from the end of the volume; if you reduce the volume size anyways, those files are lost and the OS system volume may be damaged or corrupted and may not even boot.
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>>Increasing volume sizes is much easier/safer. If you're considering tools that claim to be able to "resize" volumes/partitions, make sure they can safely *reduce* the size of a volume, if that's what you need to do.
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>>Bearing all the above in mind, a better solution may simply be to get a bigger hard drive. If you replace a 160GB drive with a 320 or 500GB unit, you can image copy the old 160GB volume to the new drive and you'll have lots of room left over for something else. The image copy will be exactly the same as it was on the old drive so Vista64 will have no reason to complain. You may even find that a new, bigger drive is cheaper than software you may be considering, and will likely be faster than your old drive, giving you a bonus speed boost.
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>Thank you for your input. I will be reducing the size of the existing partition but hopefully won't run into issue you described.
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>I have a brand new pc with 250 Gb drive with Vista 64 Business installed. (actually when I look at the size of the drive it already only has 210 Gb free, so I suppose Vista OS took a chunk of space). I want to create a D: and E: partitions, each of about 50-60 Gb. And then have one C: for the existing Vista 64 Business and another C: for XP pro. Hopefully the software I buy for partitioning and multi-book OS start will allow me to split the existing drive into these partitions and OSs.

It would be worthwhile confirming that any software you plan to buy can reduce partition sizes as you describe. If you go that route I'd be interested in hearing about your experiences.