[metapost] sh error makempx

[jkitz at verizon.net]

Ubuntu Fiesty, TexLive2007, and metapost 1.00.

The following problem does not occur when I run from terminal, but I
would like to automate through editor external program calls.

gedit and Texmaker external program calls to metapost for plain files
work fine:

beginfig(1);
  draw unitsquare scaled 1cm;
endfig;
end.

Compiles, but when makempx is needed:

beginfig(1);
  draw btex $A$ etex;
endfig;
end.

I get the error:

sh: makempx: not found

Not sure what the source of this issue is. May not be mp as it does not
happen from terminal, only from editor calls, but any insight
appreciated. Thanks.

--John