Update: 64-bit version of Taskbar Shuffle. The one on snapfiles/download.com doesn't seem to work with 64-bit Vista. I also found a similar program, Taskix. I haven't tried it, but from what I read on a forum, it works more or less like Taskbar Shuffle.
I recently dropped back from Windows 7 on one of my laptops to Windows XP, due to crackling sounds when playing music off my USB DAC.
One of the Windows 7 features I missed the most was the ability to rearrange the open applications in my taskbar. Thankfully, someone has made an application that lets you do this in earlier versions of Windows, Taskbar Shuffle (I downloaded it from SnapFiles).
At work, I start some applications in a certain order (hour sheet@Notepad++, Lotus Notes, Domino Designer). If Notes crashes and I have open a lot of applications, I often close all other apps, to get the order back. No more of that.
Speaking of useful applications. One of my all time favorite utility applications is Launchy. It lets you launch applications at the blink of an eye. Highly recommended if you prefer your keyboard to your mouse.
Clipboard Recorder is a must when working with code (you can also configure it to keep a history of bitmaps).
For screen capture, I use Gadwin PrintScreen.
At home, avast keeps me safe from viruses, and SUPERAntiSpyware (horrible title) is used to look for spyware.