A. There is a rule of thumb - rent if you might move in 3 years or so, because don't forget all the fees, commissions, and closing costs that come with buying a property.
Local real estate pricing levels and trends also matter, as well as your tax bracket.
You can use the Rent/Buy Calculator at Trulia.com to see the graphical comparison results.
Finally, a old rule of thumb - your housing cost should be no more than 28% of your gross monthly income, housing plus other debt, 36% or less.