[Skuzzle]

as said before its the boot partition. Ubuntu writes a new 1 that uses grub (a boot loader menu)

You will need to write a new windows 1 so will need a windows disk.. **** oem recovery crap

[Sevoma]

The grub boot loader (and possibly the lilo as well) are written to mbr. The mbr has it read a file on your linux partition (usually /boot/gurb/menu.lst or something). That file contains information on how to boot off of different partitions. When you deleted your linux partition, the grub bootloader in the mbr could not find the file to do anything.