In reply to TheDrunkenBakers:
Loads of conflicting info here, I'm sure you'll leave as confused as you started!
I think a 500-1000 budget for the bike itself sounds reasonable, lower if you aren't sure you'll like it, higher if you think you will. Have you tried pootling around the streets on a cheap mountain bike? If you like that then you'll likely enjoy road biking too... I think a lot of roadies have been riding for so long they cannae remember NOT riding.
If you have roadie friends (with EXPERIENCE) see if you can rope them into helping you fit a bike. That opens the second hand market which lowers bike cost.
An alu frame with carbon forks is a nice mid level bike in that price range which, despite what some might say, could be your only bike for the rest of your life if you want. Stiffer than carbon or steel which might be SLIGHTLY less comfy on rough roads.
I would recommend going with cleat pedals (called "clipless" for complicated reasons) to start with but not a necessity. mountain bike shoes are more practical for commutes, and only work with MTB pedals (SPDs) or Eggbeaters (Crank Bro's brand).
In winter - HEAPS OF LIGHTS. Don't get the Tesco ones unless you want to get new ones every couple weeks... Some people have winter tyres with more tread. I personally just don't ride if its icy and leave it at that. High vis clothes are a good idea even in daylight. Most vests come in an attractive fluoro yellow (I imagine a lot of running kit it similar)
Clubs are often pretentious and condescending to outsiders and friendly once you're "in". Its a hard one. I was a member of two awesome clubs and one awful one. Spend a bit of time learning about drafting and riding safely in a group.
I can't stand running and love cycling, I have a friend who can't stand cycling and loves running, I have a friend who loves both. Who knows!
Important things to start with:
Good quality shorts! They're like a cyclists running shoes, taking most of the load. I ride Pearl Izumi (harder to find in the UK I've found) and Castelli (slightly more expenny)
Firm saddle! New riders so often want the super padded offering. It doesn't move properly with your body and I always find it wedges in my ar$e. Get the padding on the shorts. And yes, you'll have to build up muscles in that region.
Saddle Position! Maybe the most important and most overlooked bit of bike fitting. Bad saddle position is uncomfortable and can cause more serious damage.
Puncture Repair! Its easy and cheap to do by yourself. And it means if you get more punctures on a ride than you have spare tubes you can still get home.