They're a 17", pretty sure stock size was 215/50/17. According to the site below, all Vibes are 5x100.
http://www.discountedwheelw...attern_Reference.cfmScore!
I found some in Phoenix that are $75 each, and are supposedly in A (great) condition according to car-part.com, downside is I don't have any money for 'em

According to:
http://matrixowners.com/ind...be-gt-hub-bore-size/the Vibe's hub bore is about 54mm, and from what I can find the Fiero is ~57mm... but...
http://adaptitusa.com/referencebook.htmthat lists both cars as having the same bore size... so they may just be a direct bolt-on

Since I'm currently employed at a semi-large (probably one of the largest) parts/service centers, if I get the chance I may see if I can get the next customer with a Vibe or Matrix in the same year range to let me see if the wheels would simply bolt on