VS2008: Cannot enter key to upgrade to full version

Here is a more-or-less complete guide to upgrading Visual Studio 2008 trial to pro in Windows 7.

1. Download and install the 20-day trial of AnVir Task Manager.
2. Go to Start -> Control Panel -> Programs and Features.
3. Select Microsoft Visual Studio 2008 Professional ENU, click Uninstall/Change at the top of the list.
4. Wait for the maintenance program to launch. When it does, click "Next >>" from the FIRST screen.
5. On the SECOND screen you will see three options: "Add or Remove Features", "Repair/Reinstall", "Uninstall Microsoft Visual Studio 2008". DO NOT click ANY of them. The controls you want are hidden just under these three options.
6. Launch AnVir Task Manager as an Administrator. (If you don't do this, you won't be able to enable the controls.)
7. In the Applications tab, find Microsoft Visual Studio 2008 Setup - Maintenance Page. Right-click this item and select "Detalied Info". It may be helpful to heighten the bottom panel that appears now, if your screen is big enough.
8. In the bottom panel, click "Windows".
9. In the bottom panel, expand "Microsoft Visual Studio 2008 Setup - Maintenance Page".
10. In the list that appears, several items appear to have no name. The bottom four items, which do have names, are "Visual Studio Setup Banner". Expand the anonymous item just above these four named items.
11. In the newly expanded item, you will see a number of lines, the icons for which are grayed out. This indicates they are hidden. For each disabled line, right-click and select "Visible", then right-click and select "Enabled". Don't forget to include the item in this list labeled "Upgrade" - that is the button to submit the license key data.
12. Check your Visual Studio maintenance window (we last looked at this in step 5). You should see the controls to enter your license key there. Put in the license key and click "Upgrade".

If you get stuck at one of these steps, it's possible that your maintenance window is varied slightly from mine. Once you get the main window expanded in AnVir, nose around in the hidden controls until you see the "Upgrade" button, and then make sure all controls that are siblings of that control are enabled.

Source:
Upgrading Visual Studio 2008 from trial to full on Windows 7 Beta (Build 7000)
http://stackoverflow.com/questions/453262/upgrading-visual-studio-2008-from-trial-to-full-on-windows-7-beta-build-7000