Paul,
I don’t know anything about Vista, but maybe it is enough like XP that this will help.
To down size pictures I use Paint. It is a program that comes with MSoffice. It can be found on XP by clicking on Start then all programs then accessories. Paint will appear in the drop down menu.
Open the picture in Paint. Then click on image on the top. Then select stretch/skew. You can then in the stretch windows put in 50% in both horizontal and vertical, hit enter and the picture will be reduced by 50% in both height and width. If that is not the right size select undo under the edit menu and try again with different values.
HTH
Glen