The concerns expressed by many here about the 400W PSU in the TNN500 are valid, capacitors in power circuits do age & weaken, and imo, that PSU was never a great one. If I had an TNN500, I'd look at integrating a fanless Seasonic x460 or Kingwin STR500. iirc, there's room at the top/back (traditional ATX position) corner.
OK, so making any mods in such a classic case might be a bit daunting, but it doesn't look like you would have to do much, and if you're going to be modding the CPU & GPU mountings to accommodate newer gear, well, this should enable the case to be viable for another half decade, anyway.Edit
: BTW, I think the TNN500 cooling system is powerful enough to handle a pretty hot processor. The CPU block is heavy copper, and all the elements are robust. The TDP of the Athlon 64 3200+ in one of the TNN500s I reviewed back in 2003 (2004?) was 67W, with max load CPU temp being 55C. See... http://www.silentpcreview.com/VoodooPC_ ... n_TNN-500A
In the EPCN system, an Intel P4 630 3GHz EMT64 CPU with 84W TDP was used (and this was in the days when Intel underreported their CPU heat), with 45C max temp seen under load. http://www.silentpcreview.com/article301-page4.html
All that bodes well for the 77W TDP of IvyBridge -- and you know we never hit 77W on the AUX12V line during our testing; even OC'd I doubt they'd exceed 100W.