There will be a special edition of Legacy Of Kain: Defiance which includes part 1 and 2, and it will cost the same as the standard edition. I wasn't able to find the PC version for sale, although Eidos' web site
says there will be one.
I saw a trailer on a magazine's DVD and it looked pretty neat. It said that reviewers thought Defiance was the best of the series, which means little to me since I haven't played any of them.