Hi and welcome
This should be in the root subforum, but I will press the report buttton and ask a mod to move it for you (no need to repost).
Couple of things. You shouldnt be using astro to back up apps now you are rooted. All it does is install apps back as user apps. This means that it installs apps to /data/app which is where your market apps install to.
HTC apps are /system/apps however, so need to run from within the rom.
Titanium backup (your must have backup and restore application) would probably have been able to restore this, but its too late for that now.
Click the red link in my signature and read the adb and fastboot FAQ. Set up your PC to use it.
Put your HtcContacts.apk on your C:\ so its C:\HtcContacts.apk
Then adb push it when your phone is in recovery.
the command will be:
adb push C:\HtcContacts.apk /system/app/
This IS case sensitive. You may be able to buy root explorer to do this as you're s-off but I think for adding to system/app, adb is better