Since I have upgraded to MDT 2012 Update 1 I noticed that my drive sizes were not being formatted correctly. For example if I chose "Use Specific Size" and typed in 64GB in the Partition Properties of the Format and Partition for my OSDisk and left the rest as free space (See Partition Properties - First Picture) I was only getting approximately 62GB for an OSDisk size (The size would be off more or less depending how big/small of a drive you selected to have MDT create (See Second Picture)). I had done some digging around and found a few typos in the script.
(ACTUAL PARTITION SIZE I WAS GETTING PRIOR TO ADJUST THE CODE)
After changing the script I was getting the specific size of partition I was wanting. To correct this error open DeploymentShare-->Scripts-->Open ZTIDiskPart.wsf with notepad and look for the following near the bottom...
Elseif ucase(PartitionSizeUnits) = "TB" then
GetPartitionSize = PartitionSize * 1000 * 1000
Elseif ucase(PartitionSizeUnits) = "GB" then
GetPartitionSize = PartitionSize * 1000
I replaced the "1000" with "1024" so that it was a more accurate calculation. This is what the code should look like:
Elseif ucase(PartitionSizeUnits) = "TB" then
GetPartitionSize = PartitionSize * 1024 * 1024
Elseif ucase(PartitionSizeUnits) = "GB" then
GetPartitionSize = PartitionSize * 1024
Save and close the Script and run the Deployment again and the Partition sizes should now be correct.