I need to replace a package with a custom one, which gets its own name (foo-origpackage). To allow it to be used as drop-in replacement, I added the `Provides: origpackage` line to the control file. `apt-cache show foo-origpackage` lists the "Provides" entry just fine. However, when I want to install a file depending on origpackage, it fails ("Package origpackage not installed"). 

Is there some distinction between "real" and virtual packages I'm missing?

**EDIT:**

To be precise, what I want to replace is xen-utils-common for Squeeze. My tao-xen-utils-common has the following `control` file:

```
Source: tao-xen-utils-common
Section: kernel
Priority: optional
Maintainer: Creshal <administration@tao.at>
Build-Depends: debhelper
Standards-Version: 3.8.0
Homepage: http://tao.at

Package: tao-xen-utils-common
Architecture: all
Depends: gawk, lsb-base, udev, xenstore-utils, tao-firewall
Provides: xen-utils-common
Conflicts: xen-utils-common
Replaces: xen-utils-common
Description: Xen administrative tools - common files (modified)
 The userspace tools to manage a system virtualized through the Xen virtual
 machine monitor.
 Modified for use with TAO Firewall.
```

Installing xen-utils-4.0 fails, however:

```
foo@bar# apt-cache showpkg tao-xen-utils-common
Package: tao-xen-utils-common
Versions: 
4.0.0-1tao1 (/var/lib/apt/lists/repo.tao.at_dists_stable_main_binary-amd64_Packages) (/var/lib/dpkg/status)
 Description Language: 
                 File: /var/lib/apt/lists/repo.tao.at_dists_stable_main_binary-amd64_Packages
                  MD5: 7c2503f563fca13b33b4eb3cbcb3c129

Reverse Depends: 
  tao-firewall,tao-xen-utils-common
  tao-firewall,tao-xen-utils-common
Dependencies: 
4.0.0-1tao1 - gawk (0 (null)) lsb-base (0 (null)) udev (0 (null)) xenstore-utils (0 (null)) tao-firewall (0 (null)) xen-utils-common (0 (null)) xen-utils-common (0 (null)) 
Provides: 
4.0.0-1tao1 - xen-utils-common 
Reverse Provides: 

foo@bar# apt-get install xen-utils-4.0
Reading package lists... Done
Building dependency tree       
Reading state information... Done
The following extra packages will be installed:
  xen-utils-common
Suggested packages:
  xen-docs-4.0
The following packages will be REMOVED:
  tao-xen-utils-common
The following NEW packages will be installed:
  xen-utils-4.0 xen-utils-common
```

Edit:
```
foo@bar# apt-cache policy xen-utils-4.0
xen-utils-4.0:
  Installed: (none)
  Candidate: 4.0.1-4
  Version table:
     4.0.1-4 0
        500 <http://ftp.at.debian.org/debian/> stable/main amd64 Packages
     4.0.1-4 0
        500 <http://security.debian.org/> stable/updates/main amd64 Packages

```