Can SQL Server 2005 Evaluation be used to upgrade a system?

I have multiple development SQL Servers running Enterprise edition that I want to upgrade for application testing before upgrading our production system. All of the servers meet the hardware and software requirements for SQL Server 2005 Enterprise edition. However, when I try to install to use the SQL Server 2005 Evaluation Edition to upgrade the servers in place, I get the blocked upgrade message:

Name: Microsoft SQL Server 2000 Reason: Your upgrade is blocked. For more information about upgrade support, see the "Version and Edition Upgrades" and "Hardware and Software Requirements" topics in SQL Server 2005 Setup Help or SQL Server 2005 Books Online. Edition check: Your upgrade is blocked because of edition upgrade rules. For more information about edition upgrades, see the Version and Edition Upgrades topic in SQL Server 2005 Setup Help or SQL Server 2005 Books Online.

Can the Evaluation Edition be used to upgrade these servers or do you need the full blown version?

thanks

Sorry, upgrades are prohibited *to* the Eval edition.|||I am getting this error now myself and I don't know why. I installed the trial SQL Server Express for my boss. He then asked if I would install the trial SQL Server 2005 becuase it has more capabilities he would like to try out. So I installed 2005. He noticed that there was no management studio installed and needed. So I uninstalled it and am trying to reinstall it and am getting this error. I haven't even used the software yet! I don't know what to do!|||

I was able to continue the installation but just before I click OK to install, I see this in a window

The following components that you selected will not be changed:

Client Components

that might be why I had my original problem. That problem was the Management Studio was never installed which prompted me to reinstall the system alltogether thinking I must have not checked that installation option.

Ahh!!!