I've been using a cheap compressor and airbrushes from ebay with no tank and never really ahd any problems airbrushing. I like to think some of my stuff comes out ok, If anything it's my masking that lets it down. The key to airbrushing and hand painting is in the thinning. If you're applying paint to thick by hand brush it'll look terrible. A few thin coats is better. Likewise for airbrushing. If you're mix isn't right e.g. Tamiya paints with not enough thinner then it'll dry before it hits the model. Also wash parts in warm soapy water first (just wash the whole sprue) this gets rid of the mould release agent. Use a good primer as well such as Tamiya superfine. If you end up with a rough surface for a paint finish when it comes to putting decals on they'll silver and look unrealistic. A small list for painting a model.
Clean Parts
Primer
Paint
Gloss Coat
Decals
Gloss Coat
Weathering
Matt Coat/Gloss coat
More weathering
Loads of information out there. Have a look at Flory Models tutorials too.
I've just finished a sabre and a mig , next up is Airfixs' new Harrier GR9.
This was free hand airbrushed~

This was masked

http://s1096.photobucket.com/albums/g334/benjim1979/#!cpZZ1QQtppZZ36More Pics here