Right... I've messed about in Perl and VBScrip this morning and my findings are this... I can do what you want in VB but not in Perl. Weird... (Outlook97, btw).

#!C:/ActivePerl/bin/perl.exe
use strict;
use warnings;
use Win32::OLE;

#Tset case - I know the app is running...
my $Outlook = Win32::OLE->GetActiveObject("Outlook.Application");
my ($MAPI,$Inbox,$TestFolder,$Message,$bodytext,$newtext);
$MAPI=$Outlook->GetNameSpace("MAPI");
$Inbox=$MAPI->GetDefaultFolder(6);
$TestFolder=$Inbox->Folders("Perlmonks");
print "There are " . $TestFolder->{Items}->{Count} . " items in the in
+box.\n\n";
for my $x (1) {
    $bodytext = $TestFolder->Items($x)->Body;
    print "Message Subject:\n" . $TestFolder->Items($x)->Subject . "\n
+";
    print "Body Text:\n$bodytext\n";
    print "Replacing entire body with \"foo bar\"\n\n";
    $TestFolder->Items($x)->{'Body'} = "foo bar"; #Doesn't work..
    $TestFolder->Items($x)->LetProperty('Body',"foo bar") ; #Does't wo
+rk..
    $TestFolder->Items($x)->Save; #Doesn't make a difference!
    print "Body is now supposedly:\n\n" .$TestFolder->Items($x)->Body 
+. "\n"; #Hasn't updated!
    my $NewItem = $TestFolder->Items($x)->Copy; #Works fine    
}
[download]

And in VBScript...

'..snip...
For Each M In objInbox.Items
        Text = Text & M.Subject & vbCr
        x=x+1
    M.Body= "foo bar"      'Assignment
    msgbox M.Body          'Works perfectly
    M.Save
Next
'..snip...
[download]

I'm no expert but I couldn't get the SetProperty(property,@args,value) syntax to work in Win32::OLE... perhaps it's a bug? The VBScript/Automation of Outlook97 is pretty shoddy at the best of times. Outlook89 and above have VBA (rather than VBScript) automation, AFAIK, tho...