Tell us more about what you want to do.
Does it require resizing your system partition (or boot partition)? Does it require resizing other partitions without losing your data in them?
If you do wanna resize the boot partition, you can't do that from windows disk management. Period!!!
If you wanna resize partitions without losing data in them, you can't use windows disk management.
You can only use windows disk management when making new partitions from unallocated disk space.
Otherwise you have to rely on a 3rd party software. Partition magic is crap. Don't use it. I have lost my entire partitions full of data because of that stupid program. Acronis Disk Director, however, has proven reliable. Much much more reliable. I have changed my partition structure many many times...resizing...splitting...merging...everything...Works great!