Assuming only Vista and SB5 installed you should have installed SB5's grub to mbr thereby getting SB entry at top of list followed by Vista entry. You can use the SB5 live-dvd to "repair" grub install.
There's a way to add SB5 to Vista boot loader too. Check out google for howto.
But simplest way is to install SB5 grub to mbr.
Welcome to SB and good luck.