Sounds like there might be some confusion going on here...
The XREF manager no longer exists in 2008 (actually, I think it does, it's just hidden, like the old MTEXT editor, but there's no reason to use it). Instead, the Image Manager and XREF Manager have been combined into a single External References Manager. You can call up this manager by typing either XREF or IMAGE.
In the External References Manager, you can simply select the XREFs that are flagged as "Unloaded", right-click, and select Detach. The standard SHIFT and CTRL behavior applies when selecting multiple XREFs in this manager, so you can select all Unloaded XREFs and detach them all at once. This is built-in to Autocad.
Then there is also the Reference Manager. That is a separate program that should have been installed at the same time you installed Autocad. You must go to the Start Menu to run it. If it didn't get installed, then it sounds like something went wrong in the installation. At least, I don't remember an option for disabling the installation, unless you did a custom installation and deselected it explicitly.
The Reference Manager is useful if you need to edit XREFs in a whole bunch of drawings at once. But if you are only concerned about one drawing, the External References Manager should work just fine.
It can get confusing, since all these things - XREF manager, External References Manager, and Reference Manager - have such similar names, and people sometimes mix up the names, especially if they aren't familiar with all three.