You’re right about needing upper body strength to climb. However, the best way to get that strength is by climbing; and the easier routes really don’t require much strength at all – not even in the legs. Do yourself a favor and just get to the climbing gym or crag and go for it. As a beginner you’ll want to look for a climb rated in the 5.6/5.7 range. If you can walk up a set of stairs, you can climb one of these easier routes. I’m a total wimp and recently made my first climb on a route rated 5.9 – WAY above my beginner skill level – and was able to make it 30 feet up. Like myself and most other climbers I know, you’ll be angry at yourself for not getting into climbing sooner.