Windows 7 Tip: 
There have been a lot of attempts at a great Twitter desktop client, but most have have resulted in glorified readers or overly complex applications—not a great experience. Meet blu. Now you can experience Twitter in a whole new way. If you have Windows Vista or Win7, than you have to try it was so cool and best twitter client.
See Also: Free Twitter Themes
See Also: Backup your Twitter Data to your PC
Blu is a brand new Twitter client where the design has been the main focus. It requires Microsoft .NET Framework 3.5, which means it’s a Vista and Windows 7 only release. It looks like a Mac product, too. The only downside is that this reliance on .NET Framework 3.5, means that it requires a significant amount of memory just to send and receive basic Twitter notes. This will probably improve as the application develops.
Download Blu Twitter Client here
Sorry, but Blu will run on XP you just have to have .Net 3.5 framework installed. .Net 3.5 is not limited to only being installed on Vista/Win7. Yo can go here (http://www.hanselman.com/smallestdotnet) to find out what you need to download to get your computer updated to the latest version of .Net
Really, when will people realise that you dont need vista to run .NET framework 3.5. Check your statements before u write rubbish like that please.