Here is my question.  Lets say a foreigner comes into the US.  He is not a US citizen. He gets arrested for something.  Is he protected by our Constitutional rights?  Can he take the 5th?

This is a very grey area and the legal opinion has changed over time. The general rule seems to be that all unalienable or god-given rights are applicable to everyone. Else, we could not say that these were unalienable rights. Priviledges are not and therefore may not be extended to foreigners.

Liberals want to fully extend the constitution to foreigners and illegal aliens as it suites their agenda. Conservatives tend to take a more restrictive approach.

That's the 14th amendment, section 1. Look at the last statements: "...nor deny to [u]any person[/u] within its jurisdiction the equal protection of the laws."

With that said, I would say that he does have the same protections. Didn't say I liked it, that's just how it is. And hey, if you got busted on trumped up charges in a foreign country, wouldn't you demand the same legal protections as on of their citizens? (in addition to the right to contact your do-nothing/don't-care/go-away U.S. Embassy)