To be able to change the font size, DPI or text size in remote desktop/terminal services in server 2008 use the tool found at:
By default, Windows Server 2008, used in a terminal server \ Citrix environment, does not allow standard users to change their font sizes. There is an option available to change font sizes, but it is locked down to administrators only. This is a Windows Server 2008 feature. If you try and use the standard Windows option to change font sizes, you will be prompted to provide an administrator login name and password. Unfortunately, with Windows Server 2008 the font size-changing feature is a system-wide administrative feature, rather than an individual user feature as it was in Windows Server 2003 – impacting terminal server \ Citrix environments.
To compensate for this loss of functionality for users, a tool has been produced that users can use to change font sizes! – called ‘RDFontSize’.