Can't Boot from Vista

[Guest Ernesto]

Scenario

Laptop comes with preinstalled Vista

My old Scanner doesn't run in Vista

I create a new partition (D), planning to install XP here

After installing, Xp defines (D) as the "boot" partition, meaning that I can

no longer startup from Vista OS

 

What can be done?

I suppose it's only a matter of setting C (the Vista partition) to become

the boot partition...

Please help!