What to do with obsolete Entourage projects?

Since I use Entourage 2004 email client pretty much all day when I'm at work, that's what I use for my trusted system.
With Entourage I can parcel emails, notes and other files all under the same project heading.
That bit's great.

But what to do when I've completed the project?
If obsolete projects are left in my project list, that list soon gets unweildy.
But I don't want to destroy my obsolete projects. I want to keep them intact. Those conveniently grouped files will surely come in useful someday.

When I'm finished with a project I'm tempted to archive each of them as a "Job#xxx:Completed" file but that still seems messy don't you think?

I just wonder if I'm missing some vital tenet of the GTD methedology. Might there be a better way to archive obsolete projects so that I could avoid cluttering up my list of _active_ projects?