Make a nandroid backup of your current state ROM. Next, install adw.launcher from the market. Next, make a backup of your LP homescreens and settings. Then, use root explorer and navigate to system>app. Then click the mount rw button at the top of the screen. Next, find launcherpro.apk, longpress it, select delete. REBOOT YOUR PHONE (your changes will not take effect until you reboot!). Once your phone has rebooted, install LP from the market and open it. Then restore your homescreens and settings. Replace all your widgets and your good to go.
I am doing this right now and do not guarantee it will work! That is why you need to always make nandroid backups.
Kratos