You can install PS 4.0 on top of a PS 3.0 server. This service pack brings the PS 3.0 servers up to PS 4.0 level without activating the new features of PS 4.0. It is essentially the same as the old Service Pack 3 / Feature Release 3 implementation where you upgrade to the latest service pack without activating the new features. Once 2005.04 is installed, you can only install PS 4.0 hotfixes and service packs on the PS 3.0 server. There is also no way to uninstall 2005.04. By the way, the readme for PS 4.0 says: MetaFrame Service Pack 4 Required on Servers running MetaFrame Presentation Server 3.0 Citrix does not recommend mixing servers running MetaFrame Presentation Server 3.0 and 4.0 in the same farm. However, if you must install MetaFrame Presentation Server 3.0 and 4.0 on servers in a single farm, make sure you update your servers running MetaFrame Presentation Server 3.0 to Service Pack 4. [#109701] I have no idea what Service Pack 4 is. My guess is that the readme is incorrect and it is actually referring to MetaFrame XP Feature Release 3 Service Pack 4 but I do not know for sure. Service Pack 2005.04 is the first service pack released for PS 3.0 so I don't think that is service pack 4. The .04 refers to the month in which it was released. _____ From: thin-bounce@xxxxxxxxxxxxx [mailto:thin-bounce@xxxxxxxxxxxxx] On Behalf Of Schneider, Chad M Sent: Thursday, May 12, 2005 8:13 AM To: 'thin@xxxxxxxxxxxxx' Subject: [THIN] Downloading Citrix PS 4.0 Found this note.... NOTE: This image also includes Service Pack 2005.04 for MetaFrame Presentation Server 3.0 ?? Is this the required piece we have never heard of for MPS 3.0 upgrade to 4.0? Chad M. Schneider Technology Analyst Bemis Corporate IT 920-303-7609