This should probably be put onto the FAQ, but anyways, here goes:
DT lineup on Skydancer (and before):
Anders Fridén: Vocals
Niklas Sundin: Guitars
Mikael Stanne: Guitars & backing vocals
Martin Henriksson: Bass
Anders Jivarp: Drums
IF lineup on Lunar Strain:
Mikael Stanne: Vocals
Jesper Strömblad: Drums & guitars
Glenn Ljungström: Guitars
Carl Näslund: Guitars
Johan Larsson: Bass
So, Mikael Stanne was a member of DT, who just did "guest-vocals" on Lunar Strain (not on Subterranean, that's a completely different guy). Now, some time after Skydancer was recorded, Anders Fridén left DT (but did not join IF yet) and Mikael switched to vocals only (and Fredrik Johansson joined DT at guitars) - with this line-up they did all the following recordings up to and including Projector. IF, on the other hand, had lots of member-changes during that time and finally right before The Jester Race was recorded, Anders Fridén joined the band.
I hope this cleared things up a little.
-Villain (the Doc)