You need to root the device. craigcrawford1988 wrote a guide for that ->
http://androidforums.com/motorola-milestone/75460-milestone-2-1-update-root-guide.html
Then you need to install RootExplorer on your device (google it or buy it from the market - if you can't find it send me a PM and I'll help). After that you navigate to system/app (using RootExplorer) and Mount that for R/W. Then you can use Menu - Multi-select and select multiple APKs you don't need (I can give you a list of the APKs I've removed, you can also find a nice list with explanations of what each APK is for if you google a bit) and MOVE them to your SD card or computer (for backup). The main objective is to get them off the phone internal memory. They won't get loaded into the system next time you boot but if you want to use any of them again you can copy or move them back to the system/app dir, reboot the device and they'll be back.
A good thing after doing that is to clear system cache and also go into the Application manager to remove the leftovers of the system apps.
One last thing. When you copy APKs back to the system/app dir be sure to check their permissions. It should be Read - All, Write - User. (rw-r--r--)
The same goes for any APK you wish to install as a system app. Just copy them into the system/app dir, set the permissions and install them.