Hmm...first off, use Murphy'* oil soap to get all the crud off. Follow up with a trip to your local shoe shop and get some Kiwi products. I have had wonderful success with Saddle Soap, and then afterwards use Mink Oil to replenish the leather. Once it has softened up you should be able to use the automotive stuff of your choice.
If the seats were protected from the elements fairly well, you could probably get away with just the auto stuff. But if it has sat outside for a spell or two, it wouldn't hurt it at all to use the Kiwi products.
Welcome, downwardly mobile yuppies, to the dawn of the Age of Nefarious.
1993 SSEi - FrankenJinx - dead and gone.
1994 SSE (136K strong) - 180* t-stat,HD alternator, most unequipped SSE on the club, XM radio, Kenwood CD/MP3.
2006 Chevy Malibu Maxx LTZ - Custom 2.25" manifold-back exhaust w/FM-80. Probably the only Maxx with this system.