I did a search to do this and the few links that came up happened to not work. However after a few iterations and a few adjustments to the examples I did find, I managed to get it working. Create a text file and copy in the following:
Windows Registry Editor Version 5.00
[HKEY_CLASSES_ROOT\Directory\Background\shell\VS2008 Command Prompt]
@="Open VS2008 Command Prompt Here"
"Extended"=""
"NoWorkingDirectory"=""
[HKEY_CLASSES_ROOT\Directory\Background\shell\VS2008 Command Prompt\command]
@="cmd.exe /s /k pushd \"%V\" && \"C:\\Program Files\\Microsoft Visual Studio 9.0\\VC\\vcvarsall.bat\" "
[HKEY_CLASSES_ROOT\Directory\shell\VS2008 Command Prompt]
@="Open VS2008 Command Prompt Here"
"Extended"=""
"NoWorkingDirectory"=""
[HKEY_CLASSES_ROOT\Directory\shell\VS2008 Command Prompt\command]
@="cmd.exe /s /k pushd \"%V\" && \"C:\\Program Files\\Microsoft Visual Studio 9.0\\VC\\vcvarsall.bat\" "
[HKEY_CLASSES_ROOT\Drive\shell\VS2008 Command Prompt]
@="Open VS2008 Command Prompt Here"
"Extended"=""
"NoWorkingDirectory"=""
[HKEY_CLASSES_ROOT\Drive\shell\VS2008 Command Prompt\command]
@="cmd.exe /s /k pushd \"%V\" && \"C:\\Program Files\\Microsoft Visual Studio 9.0\\VC\\vcvarsall.bat\" "
Save it as VS08CmdHere.reg and double-click on it. Once in your registry, if you Shift + Right-Click at any window directory you will see Open VS2008 Command Prompt Here.
I haven't tested on 64-bit yet, I imagine all you have to do is change the Program Files to Program Files (x86).
Enjoy :)