The problem I have is I'm starting to forget the French I already knew ! That's what comes of not reading French on a daily basis, I guess, but I'm working on rectifying that.
I don't know about any actual courses you can take - I learnt it at secondary school from years 7 - 12, so I was relatively proficient. The best advice I can give, if you're on more of a budget than the Rosetta Stone program, is to pick up a few French GCSE revision guides. I've got one called The Alternative GCSE Guides - French
which covers the basics of French and is fairly funny to boot. I personally wouldn't bother with any of these foreign phrasebooks, as if you want to read your Tintin books, like you said, it's pointless knowing directions to hotels, and how to order food and how to ask for help at a garage if you have a flat tyre.
I was always told that the best way to become good at a language is to read a lot, so once you've started learning French, you could try visiting websites of newspapers, television channels, anything really that's in French. Tintin.com
has a good news report each month, aimed at French-speaking 8-12 year olds (I'd guess) which has a wide range of vocabulary you can pick up. I think the general idea is to read anything in French - including Tintin books. :o)