I read the OTN Virtualization discussion forum. There's a question about upgrading the Oracle VM Template for Oracle Enterprise Manager Grid Control from 10g R4 to 10g R5. The question was answered and you can refer to the Metalink Doc ID 805706.1.
If you don't have access to My Oracle Support, you can still prepare yourself for a smooth upgrade by applying the workarounds or fixes described in the Known Issues section of the Readme file of the Oracle VM Grid Control Template 1.0 Media Pack for x86 (32 bit, 10.2.0.4) from the Oracle E-delivery site. You don't need to download the entire template again, except for the small Readme file. Once you resolve the known issues, you simply follow the instructions provided by Oracle Enterprise Manager 10g R5 Readme to perform the upgrade.
I also want to share more information about the Oracle VM Templates relating to Oracle Enterprise Manager Grid Control.
Oracle Enterprise Manager 10g Release 5 (10.2.0.5) was released in March 2009. It introduces the Oracle VM Management Pack, providing a comprehensive management solution that spans the entire lifecycle of applications and their virtual infrastructure, including end-to-end monitoring, configuration management, and lifecycle automation of virtualized infrastructure to capture and maximize the benefits of virtualization.
Oracle VM Templates are pre-installed and pre-configured software packaged as Oracle VM virtual machines (VMs) complete with an OS (Oracle Enterprise Linux). Oracle VM Templates for Oracle Enterprise Manager Grid Control 10g R5 (10.2.0.5) and R4 (10.2.0.4) have been provided for customer downloads from Oracle E-delivery site. Customers download and copy the software images onto the server that has Oracle VM installed on it, import and deploy the Template VMs and, after answering some one-time queries relating to the customer's desired environment within a short period of time you will have a fully installed and configured Oracle Enterprise Manager environment without having to install products from scratch. In most cases, deployment times for Oracle Enterprise Manager can be reduced from days to hours.
For new deployments, I'd recommend that you directly download and deploy the Oracle VM Templates for Oracle Enterprise Manager 10g R5 (10.2.0.5). However, users who have been using Oracle Enterprise Manager Grid Control 10g R4 (10.2.0.4) created from Oracle VM Template may want to upgrade the instance to 10g R5. The detailed instructions are documented in the Metalink Doc ID 805706.1.