Deleting Windows vista folder is next to impossible. You cannot delete it even in multiboot environment - while booting from other partition having other versions of Windows OS. Windows Vista folder contains whopping 8GB space and at times it becomes essential to claim this unused space. To reclaim this space, you need to reformate the partition and eventually face risks of data loss. In some cases, you need pricy third party tool. Here is free easy workaround for you.
Download and burn Knoppix 5.1.1 (or later) Linux live cd from here and boot your machine using this live CD.
Knoppix 5.1.1 Live CD will automatically detect and place icons for your computer’s all available harddisk partitions on Knoppix desktop. Right click and select read write mode to mount the partition which contains Windows Vista files that you want to delete. The partition will be mounted in read write mode.
Now double click over this partition’s icon to open it with Konqueror. Go to Windows Folder, right click on it and select delete. Some time it will ask for root privilege – in that case, open terminal and with sudo Konqueror command, run Konqueror in root user mode and then delete the Windows folder.