I was browsing eBay for Xterra parts last night and I came across these chips for Xterra's...anyone know about them?

Hello, and welcome to XOC.

If you search the Performance section, you'll find plenty of threads about chips. Here's just one example, from about a month ago:

web page

In short, waste of money.

Cheap resistor that fools the ECU into changing the timing...in fact it retards timing just so the ECU will advance it (IIRC).