I've deleted my Ubuntu 9.10 Linux partition, but when I'm starting Windows, I get a "grub error".
What should I do to run Windows XP and Windows 7 normally?
When you deleted the linux partition, rest of grub( stage 2 & boot menu) laying in the deleted partition is destroyed resulting in this grub error. What you got to do is remove the grub totally & make a new MBR.
Boot from win 7 installation disc, go to system repair & enter
bootsect /nt60 ALL
More on win7 procedure here
or You could boot from the winxp cd & enter this command in recovery console :
Or use linux testdisk utility & choose Write MBR option.