USB Drive Don’t Work in Vista SP1?
Here is the Fix:

The solution to this annoying problem (I had it on one PC), seems to be to locate and delete the file INFCACHE.1, which may be corrupted and causing the problem. To delete this file, you will first have to modify its permissions so the users group can access it (right-click on the
file->Properties->Security). INFCACHE.1 file. It’s located at C:\Windows\inf (scroll down to the file). (Note: to see INFCACHE.1, you must set Windows Explorer to display hidden and system files)

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or you can use this:

Resolved: USB HDD no driver issue - Vista - no drive letter

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Issue: Vista unable to find driver for external (new) 80gb western digital
drive in a Blue Ghost 2.5 Hard Disk Enclosure. All cd supplied drivers did
not work with Vista. References by device manager to “inf” being “post Win95″
and unable to install.

Partial Solution (USB Driver) found using generic driver located at

http://www.usbnews.net/news/drivers%…enclosures.htm

selecting the “win all isd” driver, download, extract and install.

Drive appeared in Disk Manager w/o letter designation, and in Device
Manager w/o designation. (admin. auth. reqd), L click Start (Vista icon) R
click Computer, L click Manage, L Continue, LL click Storage, L click Disk
Management. The drive should show as id’d by Vista. If the bar is black the
space is unallocated and the drive needs to be identified by L clicking the
smaller L disk box, then R click the larger disk box to format, partition,
etc.

Similar problems with USB thumb drives, flash drives etc. may be resolved
the same way, especially where the device appears in certain places on the
system (that means drivers are installed) but without designation, use or
functionality.

I let this problem bug me for a day without working on it, and resolved it
in about an hour after reading this forum.

Postings that helped me:

http://www.microsoft.com/windowsxp/u…nced/ntfs.mspx
http://support.microsoft.com/?kbid=310575