Will these definitely fit a '95 Z28?

http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&item=7918416995&ssPageName=MERC_VI_RSCC_Pr4_PcY_BID_Stores

Yep, they're take offs.

Ok. What size tires will fit these rims? 17" x 9"

Depends on what you want to do.
Those exact rims are for sale on this board for like $500, with 315/35/17 's on them.

I just want the cheapest ZR rated tires that will fit. Oh, what do the numbers mean? Obviously, I know what "17" is.

if you want a low price, go with 275/40/17 all around. no point in trying to squeeze a 315 on them, plus they are pricier

275 is the width in milimeters
40 is the aspect ratio, or sidewall height. The sidewall is 40% of the section width(275)
17 is the rim diameter

Thanks, dude.