Sysprep not expanding partition

I have been using sysprep with Windows 2000 for a while now. On most images it works fine, but on one perticular image it isn’t working correctly. It will read a number of things from the .inf file such as administrator password, joining the domain etc. but it won’t expand the partition to take up the entire hard drive. The Image creates a 4gig ntfs partition on a 20gig drive, I have used the extendOEMpartition parameter on other images with ntfs partitions just fine, but not this one. Has anyone seen this problem before? It is very frustrating, and does not appear to be hardware specific, I have 2 images for 1 type of machine, with 1 image when using sysprep it expands the size, with the other image it does not. Thank you