That is a good link.
However I didn't use the strict inability to interbreed which implies the inability to produce progeny or to produce only sterile hybrids in my definition. The definition I use and the one that is commonly used despite the fact that the change between one species to another is extremely gradual and thereby difficult to determine at the best of times, is the cessation of gene flow. Even though this definition is not entirely accurate when speaking of plants and definitely not with asexually reproducing species, it is useful during these debates where most are concerned with animals (Metazoans).
Whether the two groups being considered do not interbreed because of the physical limitations such as geographical location or sterile hybrids or they simply do not recognize each other as the same group, the gene flow is highly restricted. This restriction allows each group to evolve in different directions.
NOTE: John Wilkins from TalkOrigins is currently working on another FAQ further explaining the use of 'speciation' and the difference between what science means and what creationists mean and why they are wrong. As soon as it's ready I'll pass it along to PatrickHenry.
Ah, something may be stirring in the janitorial pool.