A free tool from Gourami called UNICA will uninstall every version of Citrix ICA Client from Windows 2000 and XP systems and will then open a command prompt for installing a new Citrix Client.
UNICA is tested and is known to uninstall ICA client versions from 4.0 till 11.0, on both Windows 2000 workstation and Windows XP.
To use it:
unica [commandline for unatended install for new ica client],[optional: custom message]
For example:
unica msiexec /i "\\dc01\netlogon\ica\ica.msi","Updating your ICA client"
Where \\dc01\netlogon\ica\ica.msi is a custom build installer package of your new ICA client version made with an administrative installation. (msiexec /a)
More info and download available at: http://gourami.eu/products/unica