Partiton Magic "should" do what you want, it does work with ext3 not just ext2. Ive used it before to resize & move linux partitions with out any problems, so you should be fine.

I have some USBFDs here on which I have live distribs. Is there a tool similar to Partition Magic (Windows) which allows you to dynamically enlarge Linux and related partitions on a USBFD without ...

Before you can partition your disk you'll need to squeeze your Windows partition to free up some disk space for the new partition. Head to the Disk Management tool, and right-click your main partition ...