The latter, nauseated, means to feel or suffer from nausea, as in, "I'm feeling nauseated from your perfume."
The trouble is, language is a constantly evolving thing, for better or worse, and this is one of those evolutions.
Nowadays, in the US and UK, the terms are often used interchangably. Purists might argue about that, absolutely, but historically they aren't supported.
Author and consultant for the Oxford English Dictionary, Michael Quinion, blogging at World Wide Words (http://www.worldwidewords.org/qa/qa-nau1.htm), explains.
When nauseous means "feeling physically sick", it usually appears after a verb such as feel, become, get or grow: "Doctor, I'm feeling nauseous." When it means "causing nausea", it is much more likely to be used before a noun: "To conceal the nauseous flavour of the raw spirit they added aromatic herbs and spices." Much of the older sense of nauseous, both literal and figurative, is in the process of being transferred to nauseating: "To this, with nauseating smarminess, he immediately attested", "The children looked a little green from the nauseating fairground rides." Nauseated, to judge from the citation evidence, now seems to be less common than either.
Basically, when you're not sure which to use, stick with nauseous.
Unless you're talking to a purist, as I was just the other day, when I used nauseous instead of nauseated and he called me on it.
But Professor, it was just casual conversation!