(On an iMac running 10.5.7, patched up to 1.4.6.1)
   
   I am, of course, having the very same ultra-frustrating hair mesh issues.
   In trying to sort out this issue I thought it might be helpful to report that the custom furniture I've installed works just fine (Mango & Stylist Sims).
   The majority of clothing & accessories I've downloaded do work as well, with the exception of 2 recent acquisitions which refuse to show up: Aikea's non-replacement facial piercings and some kitty ears from SimsCave/Netshow.

   Bah.