Just in case you can find SqlHelper.cs which comes in Data Access Application Block for .NET v2.
First off DO NOT try to upgrade this phone to WM5 or WM6. It simply will not work.
The best you can do is to update the firmware. I bricked my PDA so many times I do not remember what I used to bring it back to life.
Check xda-developers.com for updates.
Bluetooth Headphones
I recently got a pair of Jabra BT620s Wireless Streo Headphones but to pair them up you need to patch the PDA with this: PDA2K_BroadcomCorp_BTUpdate.zip
You now have a the ability to use Bluetooth Wireless Headphones with your PPC6600.