There's no such thing as 'Photoshop Illustrator'.
Photoshop is Adobe's raster graphics program, used primarily for editing photos, or any other manipulations of graphics composed of pixels.
Illustrator is Adobe's vector graphics program, used primarily for creating shapes (logos, line drawings, maps, etc). The graphics are composed of mathematical equations describing the length, direction, colour etc of the shapes.
So if you need to design an ad - which may consist of a number of components (photos, logos, text, etc), you may need to have Photoshop and Illustrator as well as Pagemaker in order to create it. This is why Adobe sells its programs in a 'suite' as the three programs are all used by graphic designers for different parts of their work. Each program has its particular strengths. InDesign, Adobe's newest layout application, almost manages to bundle parts of the three programs in one.
Although you probably don't have it, the best software program for clipart (including lots of borders) is Coreldraw. Buy an old copy and it will have heaps of clipart which can be used in Adobe products if you save them in the right format first (which means installing CDraw on your computer in order to do so).