I just got a project where I have to do the following on a Windows OS:

detect how many drives (C: D: E:
..etc) are connected to current
system 
what the system labels are
for each volume 
how much storage
(both used and free) for each of the
drives
what format each drive is
(NTFS/FAT32) 
how many files are
in a given directory in any of those
drives 
how big each file size is
File processing (each file is
about 2GB) where I have to do a lot
of C-like fseek(), and binary data
parsing, and big to little-endian
conversion. Have to write some logic
code as well.

I'm an experienced C\C++ programmer, but I thought this would be a perfect time for me to start learning about scripting.
Candidates that I thought of are: ( Python || Ruby ) && PowerShell.
Are those the kinds of things I can accomplish with, say, IronPython+Powershell? Or are there better tools/languages out there? 
PS: Is PowerShell meant to replace VBScript? Also, what is VB.net good for anyway now that C#, WPF, and Powershell exist?
Except for the seventh item on your list this should be fairly trivial using Powershell and WMI, as this is perhaps the natural domain for Powershell. Since you won't need another language for the first six list items it shouldn't really matter what you use for the last one. You probably can use PS (I've never done IO with it, though) or whatever suits you.
As for your second question: VBScript is probably not going to go away in the near future as the Windows Script Host is still a safer bet when writing small scripts for deployment, as it comes preinstalled on every Windows since 98. Powershell is only included in Windows 7 and later. That being said, Powershell is surely targeted at obsoleting WSH and CMD for automation purposes since it offers the same features of the aforementioned ones and much more (like easy .NET and WMI access).
VB.NET on the other hand is one of the primary .NET languages marketed by Microsoft. It has little to no relation to VBScript, is no competitor to Powershell or WPF (heck, those are completely different technologies). You may see some convergence with C# going on as both languages still seem to struggle a little finding their intended market. Still, VB.NET is the easiest choice of switching to .NET when you're a VB programmer and there were/are lots of them MS didn't want to lose just because they created .NET.
Advice for Windows system scripting+programming