Cant boot vista!

Hi, and before i start, let me apologise if I dont make the issue I am suffering clear. I am not particuarly computer literate ( I am a Mac user) Yesterday I installed Ubuntu onto an external Harddrive for use on an old laptop with no optical drive. However the laptop that i used for installation (my sisters) now wont boot back into Vista. It displays the message grub loading stage 1.5 Error 21. It appears to me that the "boot loader" for ubuntu has been installed onto her harddrive preventing windows from booting normally. This is a current HP laptop that has no recovery discs, just a recovery partition. I cannot access system recovery "F10" at start up, I get an ominous chime. I have been searching for solutions one of which seems to be downloading a vista recovery disc and selecting repair. However I cannot find a link to a download that isnt broken. HP have quoted me £35 for a recovery disc which seems a bit steep for something I would expect to be a standard feature. Any help will be gratefully recieved.