you probably didn't delete windows at all, but when you installed linux you probably overwrote the master boot record with grub. windows is likely still there, but the system has no way to know how to get there. you might be able to recover or replace the boot record with some kind of MBR utility like the Ranish Partition Manager (http://www.ranish.com/part/). Ranish should at least be able to detect the partition.