The seven books are:
Portal by Eric Flint and Ryk E. Spoor
House of Steel by David Weber
Children of the Gates by Andre Norton
World Divided: Book Two of the Secret World Chronicle by Mercedes Lackey with Cody Martin, Dennis Lee and Veronica Giguere
The Star Beast by Robert A. Heinlein<
Transgalactic by A. E. Van Vogt, Eric Flint and David Drake
The Enchanter Reborn by L. Sprague de Camp and Christopher Stasheff