Here's the latest info. I have regarding stopping ActiveSync from running on its' own. This was written for HTC Touch HD, so results may vary on TP2 and on different roms. However, it should all be the same. There may be another way, but this is the way that I know to work.
ActiveSync Auto-Run Fix
How to stop ActiveSync from turning itself on all the time
(Note: on the new official 1.56.401.0 WWE ROM,
ActiveSync does not appear to be running by itself any more. Don't know if it's just a matter of appearances though)
I've (markqld) rewritten this for the HTC HD and I works Brilliantly well. 
Thread
Active Sync can start again by itself via various scheduling routines.
There is a way to prevent this known as the "Fake Server Trick":
This 'server trick' was discovered by an Aximsite forum member known as Invid
This post originally created by IamNotMe fourpages.co.uk (Adapted by me for HD)
- Turn on your Device
- Go to Start > Programs > Activesync. This will open the Activesync program.
- Tap Menu at the bottom right hand corner of the screen. This will bring up the Options Menu. Notice the option Schedule... is greyed out? This is the all-critical option we need to get access to. But as it's disabled we can't change Activesync's default synchronisation schedule.
Ok, so how do we enable the Schedule option? Easy!!!
Fool Activesync into thinking there is an Exchange Server to sync with:
- From Activesync's Menu tap on Add Server Source.
- Enter any email and untick box then click next.
- In the following screens you can enter any old garbage. It does not matter, but just in case your unsure, just type the following in the indicated boxes
- Server Address: fake
- Leave box ticked and Tap Next
- User name: fake
- Password: fake
- Domain: fake Leave box ticked and Tap Next
- Untick all of the 'Data you want to synchronise' options
- Tap Finish
- Ok, we're done creating the server. You should now see in Activesync's main screen your normal Activesync connection(s), and a new connection called Exchange Server.
- Go back into the Menu, and lo and behold the Schedule option is now enabled! Go ahead and tap it!
- You will see that both options in the Schedule screen may be set to Every 5 Minutes
- Using the drop downs, change both the Peak times and Off-peak times boxes to Manually.
- Press the OK button at the top right of the screen.
Congratulations! Activesync is now gagged from opening on it's own and ruining your life! Your work is not done just yet though – time to clean up and get rid of the now unwanted fake Exchange Server.
- Go back into Activesync's Menu, then Tap Options.
- Highlight Microsoft Exchange, then tap Delete. A warning message will appear about removing files etc, but as you have no files associated with the fake Microsoft Exchange, it's nothing to worry about – just tap Ok.
- The list will now only show your remaining PC Sync connection(s). Obviously do not delete these!"
Note: some users say it works better if you leave the fake server there (undeleted). Not the case for me, however, it does no harm to leave it undeleted as it is totally inactive and has no effect.
PS. If you connect your HD to your PC with USB cable, ActiveSync will start automatically and everything will sync up as usual (I tried it). But after you disconnect, click the Task Manager button at top right corner of HD Flo home screen and tap the X next to ActiveSync to close active sync.
or
If you want your Activesync to work but turn off each time you disconnect your USB sync cable, load the app called Activesync Killer into internal memory.
My Results: Processor & working memory usage is significantly decreased, battery lasts longer and ActiveSync is not trying to sync all the time.