I was playing around with some USB Flash/Thumb drives I had laying around trying to find which one of them was ReadyBoost capable in Windows Vista to finally give this great feature a shot. Out of the three that I tried, my SanDisk 2GB Cruzer Micro was the only one capable. These drives come with U3 Smart Technology in a Read-Only partition. I realized I didn't use included portable apps at all so I wanted to get rid of that partition; but I simply couldn't go to Disk Management and "Delete Volume".

Luckily, SanDisk provides a tool called U3 Launchpad Removal Tool that will take care of that for you. So I format the whole thing and now I have one whole volume/partition/drive (take your pick) but now Vista didn't recognize the device as ReadyBoost capable; I was nothing but confused.

I began doing some research and I found a fix in a SanDisk community forum. You can fix this by tweaking the registry. You can format the flash drive if you haven't already done so but, correct me if I'm wrong, I don't think you need to go as far as formatting. Make sure you have removed it from your computer.

Go to the following registry key:
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\WindowsNT\CurrentVersion\EMDMgmt

*NOTE: Backup that registry key before making any changes. I'm not responsible for whatever damage you cause to your computer.

Now, in the forum they said to remove all the subkey values that are there, but I looked closely at the key names and they were a bit more descriptive and let you know more or less the device that the key pertains to. They look like this:

_??_USBSTOR#Disk&Ven_SanDisk&Prod_U3_Cruzer_Micro&Rev_3.27#
000015672B618527&0#{53f56307-b6bf-11d0-94f2-00a0c91efb8b}_1023934763

You may see several of these and others will simply contain the words "USB", "Flash", and "Drive"; you can safely delete them. Close the Registry Editor. Then re-insert the flash drive. You can ignore or close whatever Autoplay popup emerges. Re-open regedit and change the following values in the registry key that Vista has just created for your flash drive (it might even contain the name as mine did). Double-click the values to change:

"CacheSizeInMB"=dword:000003c0
"CacheStatus"=dword:00000001
"DeviceStatus"=dword:00000002

Then close Registry Editor again and, in My Computer, right-click your flash drive. Go to the ReadyBoost tab and set the cache size as you like. Good luck!