While creating and editing a database in SQL server 2008 I soon ran into a brick wall, or a 'by design' feature of the Database Management Studio.
When you design a table in a database and then try to make a change to a table structure that requires the table to be recreated, the Database Management Studio will not allow you to save the changes.
This is caused by a configuration setting that default results in the following dialog:

Error dialog

This dialog states: "Saving changes is not permitted. The changes you have made require the following tables to be dropped and re-created. You have either made changes to a table that can't be re-created or enabled the option Prevent saving changes that require the table to be re-created."

You can only react clicking the Cancel button.
And than Management Studio shows this dialog:

So what you want to do to configure the setting with the value you want (IMHO should be the default setting!).
Go to: Tools > Options

Tools menu choose Options

Select the tab Designers and choose Tables and designers

And uncheck the option: "Prevent saving changes that require table re-creation".
Once you now save changes it will work.

Henry Cordes
My thoughts exactly...

I wanted to start using SQL server 2008 on my dev machine.

I removed all sql server 2005 installations and Visual Studio 2005 (BI Tools).
I am running vista 64 bit, so I install SQL Server 2008 64 bit.
I needed to install sql server 2008 on another drive than the default suggested 'C:\Program Files\Microsoft Sql Server\'. The drive and path I wanted to use was 'D:\Program Files\Microsoft Sql Server\'.
During setup (when selecting features), I received the following error : "The INSTANCESHAREDWOWDIR command line value was not specified. This value must be specified when the INSTANCESHAREDDIR value is specified."
Yeah, I know this is really helpfull, don't you agree...
It appears that this error only occurs if I select an install dir different from the default one (C:\Program Files\Microsoft Sql Server).

I found a work-around:

1. Run the setup, select all the features you want to install. DO NOT change the install folder, press next 
2. When you see the screen displaying the configuration summary (just continue the setup untill you can copy the ConfigurationFile.ini path)
3. Copy/paste the  ConfigurationFile.ini file on the drive/folder you want to use for installation
4. Edit this file to set correct values for INSTALLSHAREDDIR & INSTALLSHAREDWOWDIR (for my case I set D:\Program Files\Microsoft Sql Server and D:\Program Files\Microsoft Sql Server (x86))
5. This step was neccesary because I want to use mixed mode authentication, if you also want to use mixed mode authentication you have to add the sa password to the ini file:
    If you have: SECURITYMODE="SQL"
    Add this entry to the file:
    SAPWD="<Password>"
6. Run setup from the command line : setup.exe /q /action=Install /configurationfile=<Path to your custom .ini>
    In my case, I first did a 'G:' and than an '<ENTER>' in the command prompt to navigate to the SQL Server 2008 installation Drive, than I entered:
    setup.exe /q /action=Install /configurationfile="D:\Program Files\Microsoft Sql Server\ConfigurationFile.ini"
    <ENTER>
    Note : the /q stands for silent mode. I didn't try without this switch.

The setup build I used was:  10.00.1600.22.

In the end I succesfully installed SQL server 2008 on my dev machine, but it took me a lot longer than initially was the plan.

Henry Cordes
My thoughts exactly...