Hi Everyone,
A few bits of info...
There is already a project on codeplex called "Arduino To Visual Studio Converter" for express users. It's not like the Visual Micro plugin but does create a vs express project from an arduino sketch.
Over the next few months Visual Micro will become 2008 and 2010 Express compatible. So it's okay to go with vs pro via the websitespark or other ms offer for now 
VS 2008 is certainly more consistently faster. I do run vs 2010 on my netbook and it's okay but I do ensure that as many vs tool windows as possible are closed. Certainly the start page is switched off and I never show the ui builder "tool box" except when/if I am using it. Only open the class viewer when needed. There are a number of vs extensions and addins that cause startup delays so install as few as possible. You need 2 GB of ram for 2010 and prob only 1GB for 2008.
For anyone starting out in the search for an ide, best of luck with whichever route you take