I have been messing around with different Window Styles and with setting the transparency of windows created with Win32::GUI.
The following code demonstrates a few of the things I have been able to pull together from my research. I had to use the Win32::API module to help with setting the transparency stuff.
Usage:
The first argument is the style index number. This defaults to 0.
The second argument (optional) is the percent of transparency you want the window to be.
Example:
c:\>windemo.pl 4 65
This would set the style to "borderless rounded" and make the window 65 percent opaque.

Feel free to play around with it and add to it. I look forward to seeing your permutations

#!perl
#windemo.pl
#Created by Steve Lloyd,  http://www.basgetti.com
#Feel free to modify and use this code as you wish.
use strict;
use Win32::GUI;
use Win32::API;
my $MainWidth=400;                    #Width of Window
my $MainHeight=400;                #Height of Window

my @styleStrings=(
    "WS_SYSMENU WS_MINIMIZE WS_MINIMIZEBOX WS_MAXIMIZE WS_MAXIMIZEBOX"
+,        # Normal Window
    "WS_SYSMENU WS_MINIMIZE WS_MINIMIZEBOX WS_MAXIMIZE WS_MAXIMIZEBOX 
+WS_VSCROLL",        # Normal Window with vertical scroll
    "WS_SYSMENU",    # Only System Menu and Close
    "WS_SYSMENU WS_MINIMIZE WS_MINIMIZEBOX",    #System Menu, Close, a
+nd Minimize
    "borderless rounded",    #Borderless Window (no Menu) with a round
+ed edge
    "borderless WS_BORDER",    #Borderless Window (no Menu) with a sma
+ll sharp edge
    );
my $index=shift || 0;    #pass first argument to set what style of win
+dow to show
my $alpha=shift;        #pass second argument to set transparency perc
+ent (0-100)
if(!defined $styleStrings[$index]){$index=0;}
my $styleString=$styleStrings[$index];
my $MainWindow = new Win32::GUI::Window(
    -name   => "MainWindow",
    -text   => 'WinDemo.pl',
    -width  => $MainWidth,
    -height    => $MainHeight,
    -pos     => [300, 100 ],
    -style     => &setWindowStyle($styleString),
    -topmost=> 1,
    );
$MainWindow->AddButton(
            -text    => "Close",
            -name    => "MyButton",
            -pos     => [10, 10 ],
            -size    => [100,20],
            -tip    => "Close this window",
            );
$MainWindow->AddTextfield(
            -text        => $styleString,
            -name        => "MyStyle",
            -pos         => [10, 110 ],
            -size        => [360,30],
            -readonly     => 1,
            );
if(length($alpha)){&makeTransparent($MainWindow,$alpha);}
$MainWindow->Show();
my $dialog=Win32::GUI::Dialog();
sub MyButton_Click{
    return -1;
    }
sub setWindowStyle{
    my $str=shift;
    my %Style=(
        WS_BORDER => 0x800000,
        WS_CAPTION => 0xC00000,
        WS_CHILD => 0x40000000,
        WS_CLIPCHILDREN => 0x2000000,
        WS_CLIPSIBLINGS => 0x4000000,
        WS_DISABLED => 0x8000000,
        WS_DLGFRAME => 0x400000,
        WS_GROUP => 0x20000,
        WS_HSCROLL => 0x100000,
        WS_MAXIMIZE => 0x1000000,
        WS_MAXIMIZEBOX => 0x10000,
        WS_MINIMIZE => 0x20000000,
        WS_MINIMIZEBOX => 0x20000,
        WS_OVERLAPPED => 0x0,
        WS_POPUP => 0x80000000,
        WS_SYSMENU => 0x80000,
        WS_TABSTOP => 0x10000,
        WS_THICKFRAME => 0x40000,
        WS_VISIBLE => 0x10000000,
        WS_VSCROLL => 0x200000,
        );
    $Style{WS_CHILDWINDOW} = $Style{WS_CHILD};
    $Style{WS_ICONIC} = $Style{WS_MINIMIZE};
    $Style{WS_OVERLAPPEDWINDOW} = $Style{WS_OVERLAPPED} || $Style{WS_C
+APTION} || $Style{WS_SYSMENU} || $Style{WS_THICKFRAME} || $Style{WS_M
+INIMIZEBOX} || $Style{WS_MAXIMIZEBOX};
    $Style{WS_POPUPWINDOW} = $Style{WS_POPUP} || $Style{WS_BORDER} || 
+$Style{WS_SYSMENU};
    $Style{WS_SIZEBOX} = $Style{WS_THICKFRAME};
    $Style{WS_TILED} = $Style{WS_OVERLAPPED};
    $Style{WS_TILEDWINDOW} = $Style{WS_OVERLAPPEDWINDOW};
    #uppercase the string coming in
    my $ustr=uc($str);
    #if the string matches a value in the hash, return the hash value
    if(defined $Style{$ustr}){return $Style{$ustr};}
    #split the string up and do a little fuzzy logic to determine what
+ they want
    my @parts=split(/[\ \t\;\:\,]+/,$str);
    my $rval;
    foreach my $part (@parts){
        if($part=~/^borderless$/is){$part="WS_POPUP";}
        elsif($part=~/vscroll/is){$part="WS_VSCROLL";}
        elsif($part=~/hscroll/is){$part="WS_HSCROLL";}
        elsif($part=~/rounded/is){$part="WS_THICKFRAME";}
        my $upart=uc($part);
        if(defined $Style{$upart}){
            $rval=($rval | $Style{$upart});
            }
        }
    return $rval;
    }
sub makeTransparent{
    #usage my $ck=makeTransparent($MainWindow,35);
    my $Window=shift || return 0;
    my $pcnt=shift || return 0;
    #Get handle of object passed in
    my $topHwnd=$Window->{-handle};
    #Convert percent value to alpha value
    my $alpha=int(($pcnt/100)*255);
    #Set some varialves
    my $WS_EX_LAYERED = hex(80000);
    my $GWL_STYLE = (-16);
    my $GWL_EXSTYLE = (-20);
    my $LWA_COLORKEY = 1;
    my $LWA_ALPHA = 2;
    my $GetWindowLong = new Win32::API("user32","GetWindowLong",['N','
+I'],'N') || return $^E;
    my $SetWindowLong = new Win32::API("user32","SetWindowLong",['N','
+I','N'],'N') || return $^E;
    my $SetLayeredWindowAttributes = new Win32::API("user32","SetLayer
+edWindowAttributes",['N','N','C','N'],'N') || return $^E;
    my $ck = $SetWindowLong->Call($topHwnd, $GWL_EXSTYLE, ($GetWindowL
+ong->Call($topHwnd, $GWL_EXSTYLE) | $WS_EX_LAYERED));
    my $alphaValue=chr($alpha);      #0 to 255, where 0=transparent an
+d 255=opaque
    $ck = $SetLayeredWindowAttributes->Call($topHwnd, 0, $alphaValue, 
+$LWA_ALPHA);
    return $ck;
    }
exit;
[download]