The basic idea is to edit one of the setup files in the ISO to insert your purchased product key, replacing the trial key, before installation. There are a few ways to do this.

1. If VS2008 (SP1) is already installed, uninstall it. You don't have to uninstall *everything* that is installed as part of the package, just the main VS2008 program.

2. Some options for editing the ISO:

a.) Extract the ISO to a directory, edit the file, then run the install from there or burn the directory to DVD and run it; or create a new ISO from the directory to mount and run, or burn and run.

b.) Use a program like MagicISO or UltraISO to directly edit the file in the ISO and save it. Then mount and run, or burn and run.

The file you need to edit is

<root>\Setup\setup.sdb

Find the [ProductKey] section and replace the trial key with your purchased key.

3. Reinstall VS2008, followed by SP1.