In answer to the OP: I guess it depends how musical you are, and how original you want to be and what your budget is.

For instant gratification you could go for SmartSound Professional Quality Music Libraries and choose one of their 'cinematic' packs.

Then if you have a musical ear you could possibly construct something out of some of the orchestral loops in GarageBand (If you have access to a mac) or one of their expansion loop libraries.

If you are musical and have the time to learn it you could go for a full blown DAW package like Steinberg Nuendo/Cubase or Apple Logic, or even the excellent but cheap Reaper.
Then you will need an orchestral VST library (Like EWQL Symphonic Orchestra, or Garritan Personal Orchestra) But now, you need to know about composition, orchestration etc and also about recording sound engineering, etc. These skills have taken me years to get to grips with and I would say I am far from excellent.

However, with perseverance and some help, I achieved this thing using Garritan Personal Orchestra (which is frankly amazing and allows you to create quite believable orchestral arrangements) and Cubase: Star Theme