And because this question will come up next..... To install this OS make sure the BB is not plugged in and follow these steps:
1. Download and install to your PC Desktop Manager 4.2 SP1 from Here
2. Download and install to your PC the OS posted above from Here
3. Delete vendor.xml from your PC's hard drive located in c:\program files\common files\research in motion\apploader
*Note: Step 3 is not always necessary but ensures that the OS will install on any brand of 8800 (currently Cingular's is all that's available)
4. Plug in BB and Open Desktop Manager. You will be prompted to upgrade.