FastAero is a freeware program, which you can download and run to enable Aero-like effects in Windows XP. Download the 7z file, extract it (you can use 7zip), and run the exe. FastAero does not need to be installed; the program sits in your system tray.
Note: I didn’t think it was working at first, but all currently open windows should be closed and opened again to enable the Aero effect.
Download FastAero (Mirror)