In reply to Josi:
The lycra makes you look like a complete numpty when you aren't riding a bike, but then so do swimming trunks when you aren't swimming and climbing shoes when you aren't climbing. Cycling clothes are designed for the activity and are well worth getting. A hard saddle + padded shorts is definitely the way forwards.
If the saddle is too low you will get sore knees. When your heel is on the pedal your leg should be straight but your knee should not be locked. Handlebars should be about the same height as the saddle, a bit higher for relaxed riding, a bit lower for racing. If you go for bang-on the same height it is a good compromise, once you get used to the position you won't like changing it! Same goes for saddle to handlebar length. Don't tip the handlebars down as far as they do in the shops, that's for chumps and Triathalosers (:P) only.
Take it easy the first few rides, otherwise you'll get put off. Try to ride on nice days!
A lot of beginner roadies try to cycle in too high a gear all the time. A cycling coach will talk loads about "pedaling circles rather than squares," (It actually makes a bit of sense once you start pedaling circles) and one of the easiest ways to do this is ride at a slightly lower gear. Lower gears also make recovery faster. Stand up as little as possible on hills, try not to jerk your shoulders and neck around too much. A cyclist whose neck and shoulders are moving all over the place either has bad technique or is absolutely knackered.
Remember that road bike brakes aren't as good as mountain bikes! Until you know how the bike handles, brake early and cautiously!
Keep your tyres pumped up to about 10psi below their maximum. Keeping them pumped up reduces chances of punctures. You should need to top them up about once a week. A good floor pump makes this very easy. If your tyres are pumped up and you still get loads of flats it might be time to change the tyres. Learn to fix inner tubes yourself to save LOADs of money. Use plastic rather than metal tyre levers.
Oil your chain once a month in dry and once a week in wet weather. try to get oil only on the chain, no need for gunk buildup on everything else.
For everything you will ever want to know about bikes,
http://sheldonbrown.com/
To fix pretty well anything,
http://www.parktool.com/blog/repair-help
You might be able to tell that I'm a bit keen on bikes. You can always drop me an email if these resources don't answer your question. I was a professional mechanic for a few years and have been riding, tinkering with and collecting bikes my whole life.
