Lord of the Rings™ to become Free-To-Play from September 2010.

[Lydon]

Once those 45 days are up, will there still be a pay-to-play version, or will it be superseded by the free-to-play edition.

Is it possible to go it alone, or does one need to join a party to survive the wrath of the Sour One?

Well, if you buy it now, the game will still be pay-to-play, as the free-to-play version is only launching around September or so, which is more than 45 days away

But to answer your question regarding paying customers, the differences between accounts etc, check out this chart Turbine provided. It sums up the differences between the three different plans they will adopt (Free, Premium and VIP) very nicely. Customers who purchased a lifetime subscription will automatically be upgraded to the VIP plan permanently.