Creating Equations in PowerPoint
If the (optionally installed) EquationEdit program that comes with Office isn't up to your needs, there are a several alternatives.
MathType
EquationEdit as supplied with Office is really the baby sibling of the more powerful (and better supported) MathType from Design Science
They even have a tutorial on using MathType with Powerpoint and handouts from their talks and webinars.
TeX4PPT
TeX4PPT by Steve Gunn is another possibility. Here's what Steve told me about TeX4PPT:
Probably the two most commonly employed tools for presentation preparation are Microsoft PowerPoint and LaTeX/Acrobat Reader. The decision is not straightforward, since neither package is a panacea. Consequently, hybrid solutions are starting to appear. PowerPoint is probably the most straightforward but it does not know how to typeset mathematics properly. Correctly positioning expressions which contain super/subscripts, integrals, fractions and other expressions of varying heights is quite an art. The equation editor that comes with office has some limitations in this respect. Additionally, the office equation editor has a limited support for mathematics symbols, e.g. there is no support for blackboard bold, limited set operators, etc. Furthermore, if you are scientist you may well have prepared your paper using LaTeX and you will have your material in TeX form. TeX4PPT has been written to address these issues and enables you to enter TeX expressions and converts them to a native powerpoint object. TeX4PPT uses a native DVI to PowerPoint converter, providing extremely fast conversion. Additionally, the result is set using native truetype fonts under windows, providing the highest fidelity. (TeX4PPT requires PowerPoint 2002)
Steve also suggests a visit to MiKTeX if you want to learn more about TeX, LaTeX etc.