I figured i will store this on my blog since each time i scramble to google for the script to move the files. So here we are:
SELECT 'ALTER DATABASE tempdb MODIFY FILE (NAME = [' + f.name + '],'
+ ' FILENAME = ''T:\TempDB\' + f.name
+ CASE WHEN f.type = 1 THEN '.ldf' ELSE '.mdf' END
+ ''');'
FROM sys.master_files f
WHERE f.database_id = DB_ID(N'tempdb');
Copy the output of the above script and paste it in SSMS. I kind of like using the script to dynamically generate the script I need to run. Sometimes, depending of available space, I may have to move log file to another drive.

Please be sure to verify the file path used above. Otherwise, you would fail to start up the SQL server instance after you bounce the services.
If you need up in that situation. Here is what you do:
Re-start the instance in safe mode (-f startup parameter) and move tempdb. Then re-start without the parameter.
Here is an example of what that would look like:
