Blackpool has parking, but it's limited. It's about £5-£7 for the day. If you get there early then you'll be fine (Bicko will tell you more). You need to follow the signs to the Pleasure Beach to get to it, the car park is by "the casino building" which is the Ice Blast shot tower end of the park. Alternatively, park in the "Central (I think) Tourist Attractions" car park, which is a big car park about five minutes walk away. Price is actually about the same as Blackpool. Walk towards the 200 foot tall roller coaster and you'll find the Pleasure Beach (you need to cross the road by the greasy spoon).
It's actually much simpler than I've made out
Southport has a Park and Ride right next to Pleasureland. So go for the Park and Ride, pay your quid and then walk to Pleasureland - no coaster to guide your way this time
Pleasureland is open in the days on school holidays, but other than that just weekends I think - you'll need to find out exactly if you plan on going at other times. I think tickets were something like a quid each, or six for a fiver kind of thing - no wristbands, so it becomes pricey fast.
I recommend the pier at Southport though and the Penny Arcade at the end to make the trip worthwhile. Watch the show being shown on the projector in the pier building, it has some absolutely awesome footage of Pleasureland before it moved, with the only footage of some of the rides - I loved it [/geek]