I added the CPAN version of PPM to Strawberry Perl - this required XML-Parser and SOAP-Lite, both of which installed successfully. For XML-Parser, I used a version of the expat library compiled with VC++ 6. A small patch:

--- PPM.pm.orig    2007-12-29 18:00:03.234375000 -0600
+++ PPM.pm    2007-12-29 17:59:58.218750000 -0600
@@ -113,8 +113,10 @@
 
 # add -5.d to archname for Perl >= 5.8 
 my $varchname = $Config{archname};
-if (length($^V) && ord(substr($^V,1)) >= 8) {
-    $varchname .= sprintf("-%d.%d", ord($^V), ord(substr($^V,1)));
+if ($] >= 5.008) {
+    my $vstring = sprintf "%vd", $^V;
+    $vstring =~ s/\.\d+$//;
+    $varchname .= "-$vstring";
 }
 
 #
[download]

was needed for PPM.pm to get it to correctly append "-5.10" to the architecture string MSWin32-x86-multi-thread. I then installed via the ppm client the GD ppm package from the UWinnipeg Perl 5.10 repository, which worked fine.

Update: If anyone wants to try this out, I've placed an archive of the files needed for installing ppm up at http://theoryx5.uwinnipeg.ca/strawberry-perl-ppm.tar.gz; to install this, save it to the C:\strawberry directory and unpack it there. You may have to edit C:\strawberry\perl\site\lib\ppm.xml to change at least the value of BUILDDIR, indicating the temporary directory which ppm uses to build things. There's a command-line utility, ppm, supplied; type help within the ppm shell to get a list of available options.