Simply running the command will tell you what the boot settings are at the moment.

This particular machine (My work Laptop) Has windows XP installed on the C: drive and Vista on the F: Drive - The IMPORTANT thing to note is each OS has an identifier. In this case the XP identifier is called {ntldr} and the Vista Identifier is called {current}

NOTE: In a lot of online forums I've seen these labeled with GUIDS and not simple names like this this may have been in Longhorn or the Vista Beta's

Before you do anything I suggest you backup the setting - bcdedit will do this for you - the command you need is....

bcdedit /export "{drive and path}"

Should you need to restore the settings you can do so using the following command

bcdedit /import "{drive and path}"

The most common thing you will want to do is change the names on the Boot menu - Vista by default calls XP something horrible like "Earlier son of Windows" and Calls itself SOmething nice like "Microsoft Windows Vista" to Change the display names you need to run the bcdedit command now get the IDENTIFIER for the OS you want to change (remember mine were ntldr and current (see above)) then use the following syntax

bcdedit -set {identifier} DESCRIPTION "What you want to call it"

For Example this renames my XP Installation to Windows XP

And this renames my Vista Installation to Windows Vista

The next most common requirement is to alter the timeout period (thou countdown while you select an OS to boot)By default is 30 Seconds to alter this the syntax is...

bcdedit /timeout {time in seconds}

To Change the DEFAULT OS that the boot loader will boot again you will need to know the identifier of that operating system, obviously by default it will be vista but if you want to change it to another OS (In my case) my XP OS the syntax is...

bcdedit /default {identifier}

The Last Thing you might want to change is the order the Operating systems are displayed in again you will need to know the identifier and the syntax is as follows...

bcdedit /displayorder {first identifier} {second identifier} etc