try chmod a+w config.gc

Thanks ... that seems to do the trick. (I didn't try the 'attrib' command.)
But I don't understand why it was necessary to do that - given that a right click on the file in Winders Explorer, select "properties" and then de-select "Readonly" seemed to do what I wanted.

Anyway, having modified config.gc to 'define' use64bitint, I find that I get:

C:\_32\perl-5.8.8\win32>perl -V:use64bitint
use64bitint='define';

C:\_32\perl-5.8.8\win32>perl -e "print ~0"
4294967295
C:\_32\perl-5.8.8\win32>
[download]

If I had really got the 64-bit support that I was seeking that last command would have produced 18446744073709551615.

There's obviously other stuff that needs to be done. (But ++ for the help, so far, ysth)

Cheers,
Rob