Bootsek.bat is a backup of your boot sector, usually this appears when you do an upgrade from one OS to another and it backs up the origional with old OS incase you want to roll back an installation of Windows :
"When Vista Setup runs, it reads the boot sector and, if it finds a previous
version, copies it into a new file in the Root of the System Partition
(\BOOTSECT.BAK) for safekeeping until it is needed to boot the previous
operating system. If you create a dual-boot system, then each time you
reboot, the Vista system starts and gets to the operating system menu. If
you choose Vista, it continues through the BCD process. If you choose the
previous version of Windows, then BCD steps back out of the way and loads
BOOTSECT.BAK, which finds NTLDR and presents the WinXP-style menu from
Boot.ini."
http://www.microsoft-questions.com/software/aspnet/28939510/bootsectbak.aspx