Kutty,
PPT 2003, Insert - Slides from file - browse for the file - open it - click
on insert all or select the slides you want and click insert. If you want to
keep the formatting of the other presentation be sure to check Keep source
formatting.
PPT 2007, on the Home tab of the ribbon, in the slides group click on the
new slide button, at the bottom choose Reuse slides, a task pane will
appear. Browse for your file, open it, right click on a thumbnail slide and
choose insert all slides or click on the slides you want, again if you want
to keep the formatting check keep source formatting at the bottom of the
pane.
