It seems to be a common question: Why does MDT 2008 still use VBScript during OS deployments, rather than moving to something more "cutting edge" like PowerShell. So let's review a few reasons:
As time goes by, PowerShell will become more and more prevalent, so we'll revisit this periodically. At this point, it's safe to say that your VBScript knowledge will serve you well for quite some time.
Now, supporting PowerShell on the MDT/ConfigMgr server (for configuration of task sequences; importing source files for apps, OSes, drivers, patches, etc.; populating databases; etc.) makes much more sense, so we are investigating what additional PowerShell support we can provide there. (You can do some things now, as our server-side components are written in .NET.) There is nothing committed at this point, though. If you're interested in something like that, please let me know.