I think it is pretty impossible, I remember having quite a few problems years back when I lived in the UK and a lot of american websites assumed that all 'states' were 2 characters. I found it quite frustrating and ended up putting SU (for Surrey). UK addresses are pretty complex, in theory you could write "2 GU185RS" on an envelope and it would get to my old address, "2 Lovells Close, Lightwater, Surrey, GU18 5RS", which has an optional county. I guess you'd have a lot more luck with american/canadian addresses as they are more 'standard'.

The main thing is to stop user error, and something like a page/form that said 'is this your address?' with it all broken down helps.

One of our clients had a problem where people kept entering the city twice, once in the city field and once in the postal/zip field. We found out that in certain versions of netscape the table wrapped causing 'Zip:' to be on the end of one line and the textbox at the start of the next, underneath the city box. We've got no idea why people decided this meant they should enter their city twice though...

gav^