[plt-scheme] High precision timing and MrEd/OSX

A recent message on this subject got no response so I will 
try again and hopefully be clearer.

I would like to do accurate scheduling in PLT on OSX.

I could not find anything in the distribution so I wrote 
an extension based on setitimer.

This extension works well enough under mzscheme/Linux and
MrEd/Linux, and under mzscheme/OSX, but fails under MrEd/OSX.

I think this may be a problem with MrEd/OSX using SIGALRM internally.

My questions are:

1. Is the a high precision timer that already works somewhere?
2. Is there something I can do to MrEd to get this extension 
   to work as it is?
3. If I need to rewrite the extension:
     a. Is there an OSX timer that is known to work with MrEd.
     b. Is the basic design flawed (ie. should I do this 
        differently).

My inital post, with more detail, is at:

<http://list.cs.brown.edu/pipermail/plt-scheme/2004-November/007303.html>

Any help would be much appreciated.

Regards,
Rohan