After doing the upgrade I am trying to access NTFS partitions on my external hard drive but they are just not showing up. I went ahead and installed Windows 7 using Parallels, and I can access the NTFS partitions from within Windows, but not from Mac OS X. I know that Snow Leopard should be able to at least read NTFS drives, so what is going on here?
As a temporary solution until you can get NTFS to natively work, I suggest using MacFuse and ntfs3g (I've used them in Leopard and the experience is pretty seamless). To be honest, I'm pretty sure that's what Apple uses in Snow Leopard anyway. They are free, mature, open-source projects, that are also used in various Linux distributions to enable the NTFS read/write capability.
Under Windows's Device Manager, do you see the drives? Are they active?
If they are disabled / de-activated, they won't be seen or shown... I do this with my Mac partitions, since I don't want the Windows Antivirus software to be scanning those drives, nor allow a virus to damage those drives, if I do get infected.
Opps, misread the question...
Does Disk Utility see the drives? If so, what partition type is shown? Are you sure it's a NTFS partition? Did you ever install NTFS3G on your system? It could be conflicting with the standard NTFS drivers...