ahhh...It'll take about a month to get your 'legs' - the worst thing is saddle-soreness - for a few days it'll feel like you're sat on razor-blades, no matter what saddle you use...
Persevere...after a couple of months you'll be like the cycle couriers round London and Bath...
Lots of short, hard rides is the best way...go out for an hour and hammer the bike around town as hard as you can - in the saddle, out of the saddle - use a variety of gears and when you're tired, 'spin' in a low gear (i.e. pedalling fast but not going fast).