It shows that can not find PSAPI.dll after i installed ie 7 beta3 and reboot.How do i solve the problem?

I have found the same problem. Several programs doesn't work now. Then, I backed up to IE 6. The programs now work.

Read the Release Notes for a fix if you're using one of the programs that ship with their own version of psapi.dll. It's not a Windows or IE problem. The relevant bits for the lazy :

Hal Screen Reader and Supernova Reader Magnifier by Dolphin--These screen readers stop responding when users click commands from Internet Explorer’s file menu. These two programs are shipped with an older version of psapi.dll that causes the program to stop responding in Internet Explorer 7.

To work around this issue, follow these steps:

Go to the installation location for Dolphin Hal Screen Reader or Supernova Reader Magnifier.

Find PSAPI.DLL in the installation location for Dolphin Hal Screen Reader or Supernova Reader Magnifier and rename it to something else, such as PSAPIOLD.DLL. Do not rename the PSAPI.DLL file in your \\Windows\System32 directory.

Restart the computer.

The program will find the new PSAPI.DLL in the \Windows\System32 directory and function normally. Users might wish to contact the software vendor website to check for the latest updates.