Vista ReadyBoost - force ReadyBoost to work on slower media

You might be wondering why you would want to do that? Simple. Laptops with slow hard drives or desktops with slow hard drives. ReadyBoost might consider your thumbdrive to be too slow to use for ReadyBoost but you can override it if you want. It can make the difference between a usable laptop and an unusable laptop with Vista. For example, an IBM Thinkpad 600E that has had the MMC-2 CPU package replaced with a Pentium 3 CPU.

I found the "override" reference here in the comments section.

Here is what you need to do:

1. Let Vista test the ReadyBoost media, and check the "Do not retest this device" checkbox.
2. Unplug the device
3. Launch Regedit and drill down to HKLM\SOFTWARE\Microsoft\Windows NT\CurrentVersion\EMDMgmt
4. Find the key related to your device (the device vendor/name is in the key)
5. Change the following values: Device Status 0x02, ReadSpeedKBs 0x1000, WriteSpeedKBs 0x1000
6. Plug the device back in, right click on it, open 'Properties' and enable the cache.