Rosetta Stone with Tagalog (there are 2 or 3 levels, maybe more now) will help a bunch.
You won't learn slang there nor good grammar or how to construct a sentence, though it helps a lot for most common words, sentences and pronunciation of those. I think it's a superb asset.
JammyD; a little bit of Tagalog is super powerful for picking up (hookers and) regular girls. And I'll throw in that Manila it'll vary a lot, say in Ayala area - reg girls working in malls etc will be more used to being hit on by foreigners - in less touristy areas you'll have massive success. For language, well...
I mean just in some situation in the store -"Seventy-five pesos, sir" and answer with "Talaagaaa???!" usually sets them off
Knowing language or otherwise having interest in culture will say a lot of good things about you regarding girls (and guys/people). Mostly they'll assume you've learned from some sort of GF or friends, which the fluffy top-hat guy with nailpolish and 7 wristwatches once said was great stuff